[PATCH] drm/doc/rfc: SR-IOV support on the new Xe driver
Michal Wajdeczko
michal.wajdeczko at intel.com
Tue Nov 14 16:55:32 UTC 2023
On 14.11.2023 13:37, Tvrtko Ursulin wrote:
>
> On 10/11/2023 18:22, Michal Wajdeczko wrote:
>> The Single Root I/O Virtualization (SR-IOV) extension to the PCI
>> Express (PCIe) specification suite is supported starting from 12th
>> generation of Intel Graphics processors.
>>
>> This RFC aims to explain how do we want to add support for SR-IOV
>> to the new Xe driver and to propose related additions to the sysfs.
>>
>> Signed-off-by: Michal Wajdeczko <michal.wajdeczko at intel.com>
>> Cc: Oded Gabbay <ogabbay at kernel.org>
>> Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
>> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
>> Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
>> Cc: Daniel Vetter <daniel at ffwll.ch>
>> ---
>> Documentation/gpu/rfc/index.rst | 5 +
>> Documentation/gpu/rfc/sysfs-driver-xe-sriov | 501 ++++++++++++++++++++
>> Documentation/gpu/rfc/xe_sriov.rst | 192 ++++++++
>> 3 files changed, 698 insertions(+)
>> create mode 100644 Documentation/gpu/rfc/sysfs-driver-xe-sriov
>> create mode 100644 Documentation/gpu/rfc/xe_sriov.rst
>>
>> diff --git a/Documentation/gpu/rfc/index.rst
>> b/Documentation/gpu/rfc/index.rst
>> index e4f7b005138d..fc5bc447f30d 100644
>> --- a/Documentation/gpu/rfc/index.rst
>> +++ b/Documentation/gpu/rfc/index.rst
>> @@ -35,3 +35,8 @@ host such documentation:
>> .. toctree::
>> xe.rst
>> +
>> +.. toctree::
>> + :maxdepth: 1
>> +
>> + xe_sriov.rst
>> diff --git a/Documentation/gpu/rfc/sysfs-driver-xe-sriov
>> b/Documentation/gpu/rfc/sysfs-driver-xe-sriov
>> new file mode 100644
>> index 000000000000..77748204dd83
>> --- /dev/null
>> +++ b/Documentation/gpu/rfc/sysfs-driver-xe-sriov
>> @@ -0,0 +1,501 @@
>> +.. Documentation/ABI/testing/sysfs-driver-xe-sriov
>> +..
>> +.. Intel Xe driver ABI (SR-IOV extensions)
>> +..
>> + The Single Root I/O Virtualization (SR-IOV) extension to
>> + the PCI Express (PCIe) specification suite is supported
>> + starting from 12th generation of Intel Graphics processors.
>> +
>> + This document describes Xe driver specific additions.
>> +
>> + For description of generic SR-IOV sysfs attributes see
>> + "Documentation/ABI/testing/sysfs-bus-pci" document.
>> +
>> + /sys/bus/pci/drivers/xe/BDF/
>> + ├── sriov_auto_provisioning
>> + │ ├── admin_mode
>> + │ ├── enabled
>> + │ ├── reset_defaults
>> + │ ├── resources
>> + │ │ ├── default_contexts_quota
>> + │ │ ├── default_doorbells_quota
>> + │ │ ├── default_ggtt_quota
>> + │ │ └── default_lmem_quota
>> + │ ├── scheduling
>> + │ │ ├── default_exec_quantum_ms
>> + │ │ └── default_preempt_timeout_us
>> + │ └── monitoring
>> + │ ├── default_cat_error_count
>> + │ ├── default_doorbell_time_us
>> + │ ├── default_engine_reset_count
>> + │ ├── default_h2g_time_us
>> + │ ├── default_irq_time_us
>> + │ └── default_page_fault_count
>
> From the department of bike-shedding, one alternative could be to have a
> directory called defaults which avoids having to have the default_
> prefix on everything under it.
like this ?
/sys/bus/pci/drivers/xe/BDF/
├── sriov_auto_provisioning
│ ├── admin_mode
│ ├── enabled
│ └── defaults
│ ├── resources
│ │ ├── contexts_quota
│ │ ├── doorbells_quota
│ │ ├── ggtt_quota
│ │ └── lmem_quota
│ ├── scheduling
│ │ ├── exec_quantum_ms
│ │ └── preempt_timeout_us
│ └── monitoring
│ ├── cat_error_count
│ ├── doorbell_time_us
│ ├── engine_reset_count
│ ├── h2g_time_us
│ ├── irq_time_us
│ └── page_fault_count
>
>> +
>> + /sys/bus/pci/drivers/xe/BDF/
>> + ├── sriov_extensions
>
> Should this be xe_sriov_extensions or if not doesn't it need agreement
> to reserve the keyword in Documentation/ABI/testing/sysfs-bus-pci?
> Sriov_auto_provisioning too I guess.
I didn't spot in ABI documents any driver specific additions to device
that were using extra prefix, nor the "reservation" placeholders.
but if we want to go with a prefix, then maybe all our additions at
device level should have one, including already added tileT:
tile0 -> xe_tile0
or even to match existing mei file we should use "xe." prefix instead:
xe.sriov_auto_provisioning
xe.sriov_extension
xe.tile0
xe.mei-gsc...
>
>> + │ ├── monitoring_period_ms
>> + │ ├── strict_scheduling_enabled
>> + │ ├── pf
>> + │ │ ├── device -> ../../../BDF
>> + │ │ ├── priority
>> + │ │ ├── tile0
>> + │ │ │ ├── gt0
>> + │ │ │ │ ├── exec_quantum_ms
>> + │ │ │ │ ├── preempt_timeout_us
>> + │ │ │ │ └── thresholds
>> + │ │ │ │ ├── cat_error_count
>> + │ │ │ │ ├── doorbell_time_us
>> + │ │ │ │ ├── engine_reset_count
>> + │ │ │ │ ├── h2g_time_us
>> + │ │ │ │ ├── irq_time_us
>> + │ │ │ │ └── page_fault_count
>> + │ │ │ └── gtX
>> + │ │ └── tileT
>> + │ ├── vf1
>> + │ │ ├── device -> ../../../BDF+1
>> + │ │ ├── stop
>> + │ │ ├── tile0
>> + │ │ │ ├── ggtt_quota
>> + │ │ │ ├── lmem_quota
>> + │ │ │ ├── gt0
>> + │ │ │ │ ├── contexts_quota
>> + │ │ │ │ ├── doorbells_quota
>> + │ │ │ │ ├── exec_quantum_ms
>> + │ │ │ │ ├── preempt_timeout_us
>> + │ │ │ │ └── thresholds
>> + │ │ │ │ ├── cat_error_count
>> + │ │ │ │ ├── doorbell_time_us
>> + │ │ │ │ ├── engine_reset_count
>> + │ │ │ │ ├── h2g_time_us
>> + │ │ │ │ ├── irq_time_us
>> + │ │ │ │ └── page_fault_count
>> + │ │ │ └── gtX
>> + │ │ └── tileT
>> + │ └── vfN
>> +..
>> +
>> +
>> +What: /sys/bus/pci/drivers/xe/.../sriov_auto_provisioning/
>> +Date: 2024
>> +KernelVersion: TBD
>> +Contact: intel-xe at lists.freedesktop.org
>> +Description:
>> + This directory appears on the device when:
>> +
>> + - device supports SR-IOV, and
>> + - device is a Physical Function (PF), and
>> + - xe driver supports SR-IOV PF on given device, and
>> + - xe driver supports automatic VFs provisioning.
>> +
>> + This directory is used as a root for all attributes related to
>> + automatic provisioning of SR-IOV Physical Function (PF) and/or
>> + Virtual Functions (VFs).
>> +
>> +
>> +What: /sys/bus/pci/drivers/xe/.../sriov_auto_provisioning/enabled
>> +Date: 2024
>> +KernelVersion: TBD
>> +Contact: intel-xe at lists.freedesktop.org
>> +Description:
>> + (RW) bool (0, 1)
>> +
>> + This file represents configuration flag for the automatic VFs
>> + (un)provisioning that could be performed by the PF.
>> +
>> + The default value is 1 (true).
>> +
>> + This flag can be set to false, unless manual provisioning is not
>> + applicable for given platform or it is not supported by current
>> + PF implementation. In such cases -EPERM will be returned.
>> +
>> + This flag will be automatically set to false when there will be
>> + other attempts to change any of VF's resource provisioning.
>> + See "sriov_extensions" section for details.
>> +
>> + This flag can be set back to true if and only if all VFs are
>> + fully unprovisioned, otherwise -EEXIST error will be returned.
>> +
>> + false = "disabled"
>> + When disabled, then PF will not attempt to do automatic
>> + VFs provisioning when VFs are being enabled and will not
>> + perform automatic unprovisioning of the VFs when VFs will
>> + be disabled.
>> +
>> + true = "enabled"
>> + When enabled, then on VFs enabling PF will do automatic
>> + VFs provisioning based on the default settings described
>> + below.
>> +
>> + If automatic VFs provisioning fails due to some reasons,
>> + then VFs will not be enabled.
>> +
>> + If enabled, all resources allocated during VFs enabling
>> + will be released during VFs disabling (automatic
>> unprovisioning).
>> +
>> +
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_auto_provisioning/admin_mode
>> +Date: 2024
>> +KernelVersion: TBD
>> +Contact: intel-xe at lists.freedesktop.org
>> +Description:
>> + (RW) bool (0, 1)
>> +
>> + This file represents configuration flag for the automatic VFs
>> + provisioning that could be performed by the PF.
>> +
>> + The default value depends on the platform type.
>> +
>> + This flag can be changed any time, but will have no effect if
>> + VFs are already provisioned.
>> +
>> + If enabled (default on discrete platforms) then the PF will
>> + retain only minimum hardcoded resources for its own use when
>> + doing VFs automatic provisioning and will not use any default
>> + values described below for its own configuration.
>> +
>> + If disabled (default on integrated platforms) then the PF will
>> + treat itself like yet another additional VF in all fair resource
>> + allocations and will also try to apply default provisioning
>> + values described below for its own configuration.
>> +
>
> One alternative could be to expose two sets of defaults, the PF and VF
> ones. With the advantage of allowing the "admin mode" / "minimal PF" to
> be explicitly configurable instead of hardcoded. Should be more flexible.
but this "admin_mode" is supposed to be configurable, only default
setting will depend on the platform.
the only "hardcoded" values will be what is needed (or already used) by
the PF for it's basic operations (load firmwares, communication, clears)
also note that when running in "minimal PF" mode then "defaults" are not
applicable to the PF, as PF is not treated like a VF, and IMO any
customization of PF scheduling parameters should be done directly using
"sriov_extensions/pf/tile/gt/*" attributes, not inside
"auto_provisioning/defaults"
only in "non-admin-mode" the PF will benefit from the default
scheduling/monitoring attributes, as then it will be treated as "yet
another VF"
regarding regular resources, PF will always be able to use what was not
allocated to other VFs (as primary goal is to have equal allocations on
each VF, PF will take any remaining anyway)
>
> If the discrete vs integrated distinction is wanted it could simply be
> made by initialy populating (driver init) the respective defaults based
> on the platform type.
>
>> +
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_auto_provisioning/reset_defaults
>> +Date: 2024
>> +KernelVersion: TBD
>> +Contact: intel-xe at lists.freedesktop.org
>> +Description:
>> + (WO) bool (1)
>> +
>> + Writing to this file will reset all default provisioning
>> parameters
>> + listed below to the default values.
>
> Maybe this isn't required if you can say it is the responsibility of
> whoever changes the defaults to either know what they are doing, or to
> save and restore themselves if they. It is not a major concern but if
> writing kernel code can be avoided perhaps it can be considered.
true, it's optional, added only as a way to make sure no residual
changes impacts new auto-provisioning (without it we will have to ask to
reload the driver)
>
>> +
>> +
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_auto_provisioning/resources/default_contexts_quota
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_auto_provisioning/resources/default_doorbells_quota
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_auto_provisioning/resources/default_ggtt_quota
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_auto_provisioning/resources/default_lmem_quota
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_auto_provisioning/scheduling/default_exec_quantum_ms
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_auto_provisioning/scheduling/default_preempt_timeout_us
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_auto_provisioning/monitoring/default_cat_error_count
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_auto_provisioning/monitoring/default_doorbell_time_us
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_auto_provisioning/monitoring/default_engine_reset_count
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_auto_provisioning/monitoring/default_h2g_time_us
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_auto_provisioning/monitoring/default_irq_time_us
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_auto_provisioning/monitoring/default_page_fault_count
>> +Date: 2024
>> +KernelVersion: TBD
>> +Contact: intel-xe at lists.freedesktop.org
>> +Description:
>> + These files represent default provisioning that should be used
>> + for VFs automatic provisioning.
>> +
>> + These values can be changed any time, but will have no effect if
>> + VFs are already provisioned.
>> +
>> + default_contexts_quota: (RW) integer 0..U32_MAX
>> + The number of GuC context IDs to provide to the VF.
>> + The default value is 0 (use fair allocations).
>> + See "sriov_extensions/vfN/tileT/gtX/contexts_quota" for
>> details.
>> +
>> + default_doorbells_quota: (RW) integer 0..U32_MAX
>> + The number of GuC doorbells to provide to the VF.
>> + The default value is 0 (use fair allocations).
>> + See "sriov_extensions/vfN/tileT/gtX/doorbells_quota" for
>> details.
>> +
>> + default_ggtt_quota: (RW) integer 0..U32_MAX
>> + The size of the GGTT address space (in bytes) to provide
>> to the VF.
>> + The default value is 0 (use fair allocations).
>> + See "sriov_extensions/vfN/tileT/ggtt_quota" for details.
>> +
>> + default_lmem_quota: (RW) integer 0..U32_MAX
>> + The size of the LMEM (in bytes) to provide to the VF.
>> + The default value is 0 (use fair allocations).
>> + See "sriov_extensions/vfN/tileT/lmem_quota" for details.
>> +
>> + default_exec_quantum_ms: (RW) integer 0..U32_MAX
>> + The GT execution quantum (in millisecs) assigned to the
>> function.
>> + The default value is 0 (infinify).
>> + See "sriov_extensions/vfN/tileT/gtX/exec_quantum_ms" for
>> details.
>> +
>> + default_preempt_timeout_us: (RW) integer 0..U32_MAX
>> + The GT preemption timeout (in microsecs) assigned to the
>> function.
>> + The default value is 0 (infinity).
>> + See "sriov_extensions/vfN/tileT/gtX/preempt_timeout_us"
>> for details.
>
> I have a slight concern here on the usability of GuC specific tunables.
>
> Whereas one can imagine an external entity (some admin, somewhere) to
> probably pretty much understand what it means to partition the local
> memory, address space, and set the scheduling timeouts (all are intuitve
> and obvious concepts), how are they suppose to approach the GuC
> doorbells and contexts?
GuC submission is mandatory for SRIOV feature to work and both GuC
doorbells and contexts IDs are almost the same kind of resources like
memory or address space.
but agree, they might be not something that were highly visible (on
Linux we don't use doorbells at all, and we had 64K of contexts so never
worried about running out of them).
>
> It could be a matter of adding more documentation for those two, or it
> even could make sense to shove them under a guc prefix (or
> subdirectory?) to signify the fact they are implementation details and
> not a fundamental concept.
IMO "guc_" prefix would be better, as with yet another subdirectory we
might have too complex structure and GuC stuff is to some extend a
"fundamental concept" for current platforms.
>
>> +
>> + default_cat_error_count: (RW) integer 0..U32_MAX
>> + default_doorbell_time_us: (RW) integer 0..U32_MAX
>> + default_engine_reset_count: (RW) integer 0..U32_MAX
>> + default_h2g_time_us: (RW) integer 0..U32_MAX
>> + default_irq_time_us: (RW) integer 0..U32_MAX
>> + default_page_fault_count: (RW) integer 0..U32_MAX
>> + The monitoring threshold to be set for the function.
>> + The default value is 0 (don't monitor).
>> + See "sriov_extensions/vfN/tileT/gtX/thresholds" for details.
>> +
>> +
>> +What: /sys/bus/pci/drivers/xe/.../sriov_extensions/
>> +Date: 2024
>> +KernelVersion: TBD
>> +Contact: intel-xe at lists.freedesktop.org
>> +Description:
>> + This directory appears on Xe device when:
>> +
>> + - device supports SR-IOV, and
>> + - device is a Physical Function (PF), and
>> + - driver is enabled to support SR-IOV PF on given device.
>> +
>> + This directory is used as a root for all attributes required to
>> + manage both Physical Function (PF) and Virtual Functions (VFs).
>> +
>> +
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_extensions/strict_scheduling_enabled
>> +Date: 2024
>> +KernelVersion: TBD
>> +Contact: intel-xe at lists.freedesktop.org
>> +Description:
>> + (RW) bool
>> +
>> + This file represents a flag used to determine if scheduling
>> + parameters should be respected even if there is no active
>> + workloads submitted by the PF or VFs.
>> +
>> + This flag is disabled by default, unless strict scheduling is
>> + not applicable on given platform. In such case this file will
>> + be read-only.
>> +
>> + The change to this file may have no effect if VFs are not yet
>> enabled.
>> + If strict scheduling can't be enabled in GuC then write will
>> fail with -EIO.
>
> I think the semantics of this need to be documented ie. how it interacts
> with exec_quantum_ms. If it does? I am guessing that it has to otherwise
> I don't know what it would mean - presumably unused timeslices are not
> given to other entities but time just goes wasted? But it is also a
if strict scheduling is disabled and given VF has no work, then it's
execution quantum expires immediately, allowing work from next VF to be
submitted to the GPU, thus maximizing GPU load.
if strict scheduling is set but given VF has no work, then VF's
timeslice is effectively wasted, as GPU will be idle, but at the benefit
that other VFs will see no fluctuations in their interval.
if you own all VMs then you probably don't want to set this ;)
> question on over what time interval. Or that too is purely defined by
> the number of PF+VFs and their respective allocated quanta.
>
> Also, would there be benefit, assuming it is possible with GuC, to allow
> configuring it per PF/VF?
this is a policy setting, applicable per each GuC scheduler, not per PF
or VF, but moved level up here to make sure we apply same settings for
the whole device (all GuCs) in the same, otherwise it would be too messy
note that the is other related attribute named "priority" that GuC will
implement for the PF, but with later plans to extend this to VFs too.
>
>> +
>> +
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_extensions/monitoring_period_ms
>> +Date: 2024
>> +KernelVersion: TBD
>> +Contact: intel-xe at lists.freedesktop.org
>> +Description:
>> + (RW) integer
>> +
>> + This file represents the configuration knob used by adverse
>> event
>> + monitoring. A value here is the period in millisecs during which
>> + events are counted and the total is checked against a threshold.
>> + See "sriov_extensions/vfN/tileT/gtX/thresholds" for more
>> details.
>> +
>> + Default is 0 (monitoring is disabled).
>> +
>> + If monitoring capability is not available, then attempt to
>> enable
>> + will fail with -EPERM error. If monitoring can't be enabled in
>> + GuC then write will fail with -EIO.
>
> Could the docs explain if there is a downside to enabling it, which is
> probably why it isn't enabled by default? Because it does sound natural
> that adverse events should be noticed.
the problem is that the definition what should be treated as unwanted VF
activity is very blurred and depends what kind of WLs will be run on VM,
as in some scenarios some sporadic issues are just "normal"
that's why we want to expose only knobs and notification mechanism,
without enforcing any policy on firmware or PF driver level, leaving
that to the administrator
>
>> +
>> +
>> +What: /sys/bus/pci/drivers/xe/.../sriov_extensions/pf/
>> +Date: 2024
>> +KernelVersion: TBD
>> +Contact: intel-xe at lists.freedesktop.org
>> +Description:
>> + This directory holds all attributes related to the SR-IOV
>> + Physical Function (PF).
>> +
>> +
>> +What: /sys/bus/pci/drivers/xe/.../sriov_extensions/vfN/
>> +Date: 2024
>> +KernelVersion: TBD
>> +Contact: intel-xe at lists.freedesktop.org
>> +Description:
>> + This directory holds all attributes related to the SR-IOV
>> + Virtual Function (VF).
>> +
>> + Note that VF numbers (N) are 1-based as described in PCI
>> SR-IOV specification.
>> + The Xe driver implementaton follows that naming schema.
>> +
>> + There will be "vf1", "vf2" up to "vfN" directories, where N
>> matches
>> + value of the PCI "sriov_totalvfs" attribute.
>> +
>> +What: /sys/bus/pci/drivers/xe/.../sriov_extensions/pf/tileT/
>> +What: /sys/bus/pci/drivers/xe/.../sriov_extensions/vfN/tileT/
>> +Date: 2024
>> +KernelVersion: TBD
>> +Contact: intel-xe at lists.freedesktop.org
>> +Description:
>> + This directory holds all SR-IOV attributes related to the
>> device tile.
>> + The tile numbers (T) start from 0.
>> +
>> + There is at least one "tile0/" directory present.
>> +
>> +
>> +What: /sys/bus/pci/drivers/xe/.../sriov_extensions/pf/tileT/gtX
>> +What: /sys/bus/pci/drivers/xe/.../sriov_extensions/vfN/tileT/gtX
>> +Date: 2024
>> +KernelVersion: TBD
>> +Contact: intel-xe at lists.freedesktop.org
>> +Description:
>> + This directory holds all SR-IOV attributes related to the
>> device GT.
>> + The GT numbers (X) start from 0.
>> +
>> + There is at least one "gt0/" directory present.
>> +
>> +
>> +What: /sys/bus/pci/drivers/xe/.../sriov_extensions/pf/device
>> +What: /sys/bus/pci/drivers/xe/.../sriov_extensions/vfN/device
>> +Date: 2024
>> +KernelVersion: TBD
>> +Contact: intel-xe at lists.freedesktop.org
>> +Description:
>> + (symbolic link)
>> +
>> + Backlink to the PCI device entry representing given function.
>> + For PF this link is always present.
>> + For VF this link is present only for currently enabled VFs.
>> +
>> +
>> +What: /sys/bus/pci/drivers/xe/.../sriov_extensions/pf/priority
>> +Date: 2024
>> +KernelVersion: TBD
>> +Contact: intel-xe at lists.freedesktop.org
>> +Description:
>> + (RW) string
>> +
>> + This file represents a GuC Scheduler knob to override the
>> default
>> + round-robin or FIFO scheduler policies implemented by the GuC.
>> +
>> + The default value is "peer".
>> +
>> + This flag can be changed, unless such change is not applicable
>> + for given platform or is not supported by current GuC firmware.
>> + In such case this file could be read-only or will return -EPERM
>> + on write attempt.
>> +
>> + "immediate"
>> + GuC will Schedule PF workloads immediately and PF
>> + workloads only until the PF's work queues in GuC
>> + are empty.
>> +
>> + "lazy"
>> + GuC will Schedule PF workloads at the next opportune
>> + moment and PF workloads only until the PF work queues
>> + in GuC are empty.
>> +
>> + "peer"
>> + GuC Scheduler will treat PF and VFs with equal priority.
>
> Hmmm this is too very GuC specific and I wonder what is the usecase for
> lazy? Lazy = "don't care when it runs, but when it runs it will run
> everything queued so far", right? Feels a bit odd on first.
>
> "Immediate" may also not be depending on preemption granularity and
> workloads, right?
>
> Are there any ideas to express the knobs in a more generic fashion?
will talk with GuC architect to provide a better explanation.
in the meantime, we can treat that as a "placeholder" for the knob that
will provide flexibility when GuC shall attempt to submit, usually
sporadic, workloads from the otherwise idle PF.
this is important in the "admin-mode" and with "strict-scheduling" as we
don't want to waste PF's execution_quantum
if you think that it is too unstable knob, we can try to hide it in
debugfs first, expose when more mature
>
>> +
>> +
>> +What: /sys/bus/pci/drivers/xe/.../sriov_extensions/vfN/stop
>> +Date: 2024
>> +KernelVersion: TBD
>> +Contact: intel-xe at lists.freedesktop.org
>> +Description:
>> + (WO) bool (1)
>> +
>> + Write to this file will force GuC to stop handle any requests
>> from
>> + this VF, but without triggering a FLR.
>> + To recover, the full FLR must be issued using generic
>> "device/reset".
>> +
>> + This file allows to implement custom policy mechanism when VF is
>> + misbehaving and triggering adverse events above defined
>> thresholds.
>> +
>> +
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_extensions/pf/tileT/gtX/exec_quantum_ms
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_extensions/pf/tileT/gtX/preempt_timeout_us
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_extensions/vfN/tileT/gtX/exec_quantum_ms
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_extensions/vfN/tileT/gtX/preempt_timeout_us
>> +Date: 2024
>> +KernelVersion: TBD
>> +Contact: intel-xe at lists.freedesktop.org
>> +Description:
>> + These files represent scheduling parameters of the functions.
>> +
>> + These scheduling parameters can be changed even if VFs are
>> enabled
>> + and running, unless such change is not applicable on given
>> platform
>> + due to fixed hardware or firmware assignment.
>> +
>> + exec_quantum_ms: (RW) integer 0..U32_MAX
>> + The GT execution quantum in [ms] assigned to the function.
>> + Requested quantum might be aligned per HW/FW requirements.
>> +
>> + Default is 0 (unlimited).
>> +
>> + preempt_timeout_us: (RW) integer 0..U32_MAX
>> + The GT preemption timeout in [us] assigned to the function.
>> + Requested timeout might be aligned per HW/FW requirements.
>> +
>> + Default is 0 (unlimited).
>
> Alignment for the above two will be visible after read-back?
unfortunately not, as GuC does not expose any interface to query final
values (sometimes they depend on HW clocks, some are FW implementation
details, that could change with new release)
>
>> +
>> +
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_extensions/vfN/tileT/ggtt_quota
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_extensions/vfN/tileT/lmem_quota
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_extensions/vfN/tileT/gtX/contexts_quota
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_extensions/vfN/tileT/gtX/doorbells_quota
>> +Date: 2024
>> +KernelVersion: TBD
>> +Contact: intel-xe at lists.freedesktop.org
>> +Description:
>> + These files represent shared resource assigned to the functions.
>> +
>> + These resource parameters can be changed, unless VF is
>> already running,
>> + or such change is not applicable on given platform due to
>> fixed hardware
>> + or firmware assignment.
>> +
>> + Writes to these attributes may fail with:
>> + -EPERM if change is not applicable on give HW/FW.
>> + -E2BIG if value larger that HW/FW limit.
>> + -EDQUOT if value is larger than maximum quota defined by
>> the PF.
>> + -ENOSPC if PF can't allocate required quota.
>> + -EBUSY if the resource is currently in use by the VF.
>> + -EIO if GuC refuses to change provisioning.
>
> Why it would refuse if input is valid? In other words, what is the
> user/admin supposed to do on -EIO?
in early implementations we were fully relying on the GuC and return
-EIO on every error, as we didn't track the VF state that would allow us
to catch improper changes while VF is running (-EBUSY above) but even if
we (PF) do our best then GuC is still a decider here and may return
(unlikely) error.
as recovery we will be suggesting a VF FLR and then retry.
>
>> +
>> + ggtt_quota: (RW) integer 0..U64_MAX
>> + The size of the GGTT address space (in bytes) assigned to
>> the VF.
>> + The value might be aligned per HW/FW requirements.
>> +
>> + Default is 0 (unprovisioned).
>> +
>> + lmem_quota: (RW) integer 0..U64_MAX
>> + The size of the Local Memory (in bytes) assigned to the VF.
>> + The value might be aligned per HW/FW requirements.
>> +
>> + This attribute is only available on discrete platforms.
>> +
>> + Default is 0 (unprovisioned).
>> +
>> + contexts_quota: (RW) 0..U16_MAX
>> + The number of GuC submission contexts assigned to the VF.
>> + This value might be aligned per HW/FW requirements.
>> +
>> + Default is 0 (unprovisioned).
>> +
>> + doorbells_quota: (RW) 0..U16_MAX
>> + The number of GuC doorbells assigned to the VF.
>> + This value might be aligned per HW/FW requirements.
>> +
>> + Default is 0 (unprovisioned).
>> +
>> +
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_extensions/pf/tileT/gtX/thresholds/cat_error_count
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_extensions/pf/tileT/gtX/thresholds/doorbell_time_us
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_extensions/pf/tileT/gtX/thresholds/engine_reset_count
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_extensions/pf/tileT/gtX/thresholds/h2g_time_us
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_extensions/pf/tileT/gtX/thresholds/irq_time_us
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_extensions/pf/tileT/gtX/thresholds/page_fault_count
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_extensions/vfN/tileT/gtX/thresholds/cat_error_count
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_extensions/vfN/tileT/gtX/thresholds/doorbell_time_us
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_extensions/vfN/tileT/gtX/thresholds/engine_reset_count
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_extensions/vfN/tileT/gtX/thresholds/h2g_time_us
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_extensions/vfN/tileT/gtX/thresholds/irq_time_us
>> +What:
>> /sys/bus/pci/drivers/xe/.../sriov_extensions/vfN/tileT/gtX/thresholds/page_fault_count
>> +Date: 2024
>> +KernelVersion: TBD
>> +Contact: intel-xe at lists.freedesktop.org
>> +Description:
>> + These files represent threshold values used by the GuC to
>> trigger
>> + security events if adverse event monitoring is enabled.
>
> How are the security events delivered? There is mention of uevents in a
> later paragraph - are they already defined or should be together with
> this so the link can be place here?
chicken/egg problem - we don't have uevent fully defined as we were
waiting for these threshold definitions to be accepted, and without them
being available we didn't generate uevent, but in early code we had:
"THRESHOLD_EXCEEDED=1"
"THRESHOLD_ID=%#x"
"VF_ID=%u"
>
>> +
>> + These thresholds are checked every "monitoring_period_ms".
>> + Refer to GuC ABI for details about each threshold category.
>
> Is it possible to have a link here to GuC ABI?
(shared offline, as GuC spec is not public yet)
>
> Regards,
>
> Tvrtko
Thanks,
Michal
>
>> +
>> + Default value for all thresholds is 0 (disabled).
>> +
>> + cat_error_count: (RW) integer
>> + doorbell_time_us: (RW) integer
>> + engine_reset_count: (RW) integer
>> + h2g_time_us: (RW) integer
>> + irq_time_us: (RW) integer
>> + page_fault_count: (RW) integer
>> diff --git a/Documentation/gpu/rfc/xe_sriov.rst
>> b/Documentation/gpu/rfc/xe_sriov.rst
>> new file mode 100644
>> index 000000000000..574f6414eabb
>> --- /dev/null
>> +++ b/Documentation/gpu/rfc/xe_sriov.rst
>> @@ -0,0 +1,192 @@
>> +.. SPDX-License-Identifier: MIT
>> +
>> +========================
>> +Xe – SR-IOV Support Plan
>> +========================
>> +
>> +The Single Root I/O Virtualization (SR-IOV) extension to the PCI
>> Express (PCIe)
>> +specification suite is supported starting from 12th generation of
>> Intel Graphics
>> +processors.
>> +
>> +This document describes planned ABI of the new Xe driver (see xe.rst)
>> that will
>> +provide flexible configuration and management options related to the
>> SR-IOV.
>> +It will also highlight few most important changes to the Xe driver
>> +implementation to deal with Intel GPU SR-IOV specific requirements.
>> +
>> +
>> +SR-IOV Capability
>> +=================
>> +
>> +Due to SR-IOV complexity and required co-operation between hardware,
>> firmware
>> +and kernel drivers, not all Xe architecture platforms might have
>> SR-IOV enabled
>> +or fully functional.
>> +
>> +To control at the driver level which platform will provide support
>> for SR-IOV,
>> +as we can't just rely on the PCI configuration data exposed by the
>> hardware,
>> +we will introduce "has_sriov" flag to the struct xe_device_desc that
>> describes
>> +a device capabilities that driver checks during the probe.
>> +
>> +Initially this flag will be set to disabled even on platforms that we
>> plan to
>> +support. We will enable this flag only once we finish merging all
>> required
>> +changes to the driver and related validated firmwares are also made
>> available.
>> +
>> +
>> +SR-IOV Platforms
>> +================
>> +
>> +Initially we plan to add SR-IOV functionality to the following SDV
>> platforms
>> +already supported by the Xe driver:
>> +
>> + - TGL (up to 7 VFs)
>> + - ADL (up to 7 VFs)
>> + - MTL (up to 7 VFs)
>> + - ATSM (up to 31 VFs)
>> + - PVC (up to 63 VFs)
>> +
>> +Newer platforms will be supported later, but we hope that enabling
>> will be
>> +much faster, as majority of the driver changes are either platform
>> agnostic
>> +or are similar between earlier platforms (hence we start with SDVs).
>> +
>> +
>> +PF Mode
>> +=======
>> +
>> +Support in the driver for acting in Physical Function (PF) mode, i.e.
>> mode
>> +that allows configuration of VFs, depends on the CONFIG_PCI_IOV and
>> will be
>> +enabled by default.
>> +
>> +However, due to potentially conflicting requirements for SR-IOV and
>> other mega
>> +features, we might want to have an option to disable SR-IOV PF mode
>> support at
>> +the driver load time.
>> +
>> +Thus, we plan to use additional modparam named "sriov_totalvfs" which
>> if set to
>> +0 will force the driver to operate in the native (non-virtualized) mode.
>> +The same modparam could be used to limit number of supported Virtual
>> Functions
>> +(VFs) by the driver compared to the hardware limit exposed in PCI
>> configuration.
>> +
>> +The name of this modparam corresponds to the existing PCI sysfs
>> attribute, that
>> +by default exposes hardware capability.
>> +
>> +The default value of this param will allow to support all possible
>> VFs as
>> +claimed by the hardware.
>> +
>> +This modparam will have no effect if driver is running on the VF device.
>> +
>> +
>> +VFs Enabling
>> +============
>> +
>> +To enable or disable VFs we plan to rely on existing sysfs attribute
>> exposed by
>> +the PCI subsystem named "sriov_numvfs". We will provide all necessary
>> tweaks to
>> +provision VFs in our custom implementation of the "sriov_configure"
>> hook from
>> +the struct pci_driver.
>> +
>> +If for some reason, including explicit request to disable SR-IOV PF
>> mode using
>> +modparam, we will not be able to correctly support any VFs, driver
>> will change
>> +number of supported VFs, exposed to the userspace by "sriov_totalvfs"
>> attribute,
>> +to 0, thus preventing configuration of the VFs.
>> +
>> +
>> +VF Mode
>> +=======
>> +
>> +When driver is running on the VF device, then due to hardware
>> enforcements,
>> +access to the privileged registers is not possible. To avoid relying
>> on these
>> +registers, we plan to perform early detection if we are running on
>> the VF
>> +device using dedicated VF_CAP(0x1901f8) register and then use global
>> macro
>> +IS_SRIOV_VF(xe) to control the driver logic.
>> +
>> +To speed up merging of the required changes, we might first introduce
>> dummy
>> +macro that is always set to false, to prepare driver to avoid some
>> code paths
>> +before we finalize our VF mode detection and other VFs enabling changes.
>> +
>> +
>> +Resources
>> +=========
>> +
>> +Most of the hardware (or firmware) resources available on the Xe
>> architecture,
>> +like GGTT, LMEM, GuC context IDs, GuC doorbells, will be shared
>> between PF and
>> +VFs and will require some provisioning steps to assign those
>> resources for use
>> +by the VF.
>> +
>> +Until VFs are provisioned with resources, the PF driver will be able
>> to use all
>> +resources, in the same way as it would be running in non-virtualized
>> mode.
>> +
>> +If some resource (of part or region of it) is assigned to specific
>> VF, then PF
>> +is not allowed to use that part or region of the resource, but can
>> continue to
>> +use whatever is left available.
>> +
>> +Those resources are usually fully virtualized, so they will not
>> require any
>> +special handling when used by the VF driver, except that VF driver
>> must know
>> +the assigned quota.
>> +
>> +The most notable exception is the GGTT address space, as on some
>> platforms,
>> +the VF driver must additionally know the real range that it can access.
>> +
>> +Once the resources were assigned to the VF use and the VF driver has
>> started,
>> +then it is not allowed to change such provisioning, as that would
>> break the
>> +VF driver. To make changes the VF driver, which was using these
>> resources,
>> +must be unloaded (or the VM is terminated) and the VF device must be
>> reset
>> +using the FLR.
>> +
>> +
>> +Scheduling
>> +==========
>> +
>> +The workloads from PF driver and VF drivers must be submitted to the
>> hardware
>> +always by using the GuC submission mechanism. Unless VF has exclusive
>> access
>> +to the GT then submissions from different VFs are time-sliced and
>> controlled
>> +with additional "execution_quantum" and "preemption_timeout" parameters.
>> +
>> +In contrast to the resource provisioning, those scheduling parameters
>> can be
>> +changed even if VF drivers are already running and are active.
>> +
>> +
>> +Automatic VFs Provisioning
>> +==========================
>> +
>> +To provide out-of-the box experience when user will be enabling VFs
>> using
>> +generic "sriov_numvfs" attribute without requiring complex
>> provisioning steps,
>> +the SR-IOV PF driver will implement automatic VFs resource provisioning.
>> +
>> +By default, all VFs will be allocated with the fair amount of the
>> mandatory
>> +resources (like GGTT, GuC IDs) and with unrestricted scheduling
>> parameters.
>> +Such provisioning should be sufficient for most of the normal usages,
>> when
>> +no strict SLA is required.
>> +
>> +The PF driver will also expose some additional sysfs files to allow
>> adjusting
>> +this automatic VFs provisioning, like default values for most of the
>> +provisioning parameters that PF will then apply for each enabled VF.
>> +
>> + Details about those extension can be found in
>> + :download:`Preliminary Xe driver ABI <sysfs-driver-xe-sriov>`.
>> +
>> +
>> +Manual VFs Provisioning
>> +=======================
>> +
>> +If automatic VFs provisioning, which applies same configuration to
>> every VF,
>> +is not sufficient or there is a need for advanced customization of
>> some VF,
>> +the PF driver will also provide extended sysfs interface which will
>> allow
>> +control every provisioning attribute to the lowest feasible level.
>> +
>> +It is expected that these low-level attributes will be mostly used by
>> the
>> +advanced users or by the custom tools that will setup configurations
>> that
>> +meet predefined and validated SLA as required by the customers.
>> +
>> + Details about those extension can be found in
>> + :download:`Preliminary Xe driver ABI <sysfs-driver-xe-sriov>`.
>> +
>> +
>> +VFs Monitoring
>> +==============
>> +
>> +In addition to the resource provisioning or changing scheduling
>> parameters,
>> +the PF driver might also allow configure some monitoring parameters,
>> like
>> +thresholds of adverse events or sample period, to track undesired
>> behavior
>> +of the VFs that could impact the whole system.
>> +
>> +Once those thresholds are setup and sampling period is defined, the
>> GuC will
>> +notify the PF driver about which VF is excessing the threshold and
>> then PF is
>> +able to trigger the uevent to notify the administrator (or VMM) that
>> could
>> +take some action against the VF.
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