[Intel-gfx] [RFC v3 1/3] drm/doc/rfc: VM_BIND feature design document
Zeng, Oak
oak.zeng at intel.com
Tue Jun 14 21:47:50 UTC 2022
Thanks,
Oak
> -----Original Message-----
> From: dri-devel <dri-devel-bounces at lists.freedesktop.org> On Behalf Of
> Zeng, Oak
> Sent: June 14, 2022 5:13 PM
> To: Vishwanathapura, Niranjana <niranjana.vishwanathapura at intel.com>;
> Landwerlin, Lionel G <lionel.g.landwerlin at intel.com>
> Cc: Intel GFX <intel-gfx at lists.freedesktop.org>; Wilson, Chris P
> <chris.p.wilson at intel.com>; Hellstrom, Thomas
> <thomas.hellstrom at intel.com>; Maling list - DRI developers <dri-
> devel at lists.freedesktop.org>; Vetter, Daniel <daniel.vetter at intel.com>;
> Christian König <christian.koenig at amd.com>
> Subject: RE: [Intel-gfx] [RFC v3 1/3] drm/doc/rfc: VM_BIND feature design
> document
>
>
>
> Thanks,
> Oak
>
> > -----Original Message-----
> > From: Vishwanathapura, Niranjana <niranjana.vishwanathapura at intel.com>
> > Sent: June 14, 2022 1:02 PM
> > To: Landwerlin, Lionel G <lionel.g.landwerlin at intel.com>
> > Cc: Zeng, Oak <oak.zeng at intel.com>; Intel GFX <intel-
> > gfx at lists.freedesktop.org>; Maling list - DRI developers <dri-
> > devel at lists.freedesktop.org>; Hellstrom, Thomas
> > <thomas.hellstrom at intel.com>; Wilson, Chris P
> <chris.p.wilson at intel.com>;
> > Vetter, Daniel <daniel.vetter at intel.com>; Christian König
> > <christian.koenig at amd.com>
> > Subject: Re: [Intel-gfx] [RFC v3 1/3] drm/doc/rfc: VM_BIND feature design
> > document
> >
> > On Tue, Jun 14, 2022 at 10:04:00AM +0300, Lionel Landwerlin wrote:
> > >On 13/06/2022 21:02, Niranjana Vishwanathapura wrote:
> > >>On Mon, Jun 13, 2022 at 06:33:07AM -0700, Zeng, Oak wrote:
> > >>>
> > >>>
> > >>>Regards,
> > >>>Oak
> > >>>
> > >>>>-----Original Message-----
> > >>>>From: Intel-gfx <intel-gfx-bounces at lists.freedesktop.org> On
> > >>>>Behalf Of Niranjana
> > >>>>Vishwanathapura
> > >>>>Sent: June 10, 2022 1:43 PM
> > >>>>To: Landwerlin, Lionel G <lionel.g.landwerlin at intel.com>
> > >>>>Cc: Intel GFX <intel-gfx at lists.freedesktop.org>; Maling list -
> > >>>>DRI developers <dri-
> > >>>>devel at lists.freedesktop.org>; Hellstrom, Thomas
> > >>>><thomas.hellstrom at intel.com>;
> > >>>>Wilson, Chris P <chris.p.wilson at intel.com>; Vetter, Daniel
> > >>>><daniel.vetter at intel.com>; Christian König
> > <christian.koenig at amd.com>
> > >>>>Subject: Re: [Intel-gfx] [RFC v3 1/3] drm/doc/rfc: VM_BIND
> > >>>>feature design
> > >>>>document
> > >>>>
> > >>>>On Fri, Jun 10, 2022 at 11:18:14AM +0300, Lionel Landwerlin wrote:
> > >>>>>On 10/06/2022 10:54, Niranjana Vishwanathapura wrote:
> > >>>>>>On Fri, Jun 10, 2022 at 09:53:24AM +0300, Lionel Landwerlin wrote:
> > >>>>>>>On 09/06/2022 22:31, Niranjana Vishwanathapura wrote:
> > >>>>>>>>On Thu, Jun 09, 2022 at 05:49:09PM +0300, Lionel Landwerlin
> wrote:
> > >>>>>>>>> On 09/06/2022 00:55, Jason Ekstrand wrote:
> > >>>>>>>>>
> > >>>>>>>>> On Wed, Jun 8, 2022 at 4:44 PM Niranjana Vishwanathapura
> > >>>>>>>>> <niranjana.vishwanathapura at intel.com> wrote:
> > >>>>>>>>>
> > >>>>>>>>> On Wed, Jun 08, 2022 at 08:33:25AM +0100, Tvrtko
> > >>>>Ursulin wrote:
> > >>>>>>>>> >
> > >>>>>>>>> >
> > >>>>>>>>> >On 07/06/2022 22:32, Niranjana Vishwanathapura wrote:
> > >>>>>>>>> >>On Tue, Jun 07, 2022 at 11:18:11AM -0700, Niranjana
> > >>>>>>>>>Vishwanathapura
> > >>>>>>>>> wrote:
> > >>>>>>>>> >>>On Tue, Jun 07, 2022 at 12:12:03PM -0500, Jason
> > >>>>>>>>>Ekstrand wrote:
> > >>>>>>>>> >>>> On Fri, Jun 3, 2022 at 6:52 PM Niranjana
> > >>>>Vishwanathapura
> > >>>>>>>>> >>>> <niranjana.vishwanathapura at intel.com> wrote:
> > >>>>>>>>> >>>>
> > >>>>>>>>> >>>> On Fri, Jun 03, 2022 at 10:20:25AM +0300, Lionel
> > >>>>>>>>>Landwerlin
> > >>>>>>>>> wrote:
> > >>>>>>>>> >>>> > On 02/06/2022 23:35, Jason Ekstrand wrote:
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > On Thu, Jun 2, 2022 at 3:11 PM Niranjana
> > >>>>>>>>>Vishwanathapura
> > >>>>>>>>> >>>> > <niranjana.vishwanathapura at intel.com> wrote:
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > On Wed, Jun 01, 2022 at 01:28:36PM
> > >>>>-0700, Matthew
> > >>>>>>>>> >>>>Brost wrote:
> > >>>>>>>>> >>>> > >On Wed, Jun 01, 2022 at 05:25:49PM
> > >>>>+0300, Lionel
> > >>>>>>>>> Landwerlin
> > >>>>>>>>> >>>> wrote:
> > >>>>>>>>> >>>> > >> On 17/05/2022 21:32, Niranjana
> Vishwanathapura
> > >>>>>>>>> wrote:
> > >>>>>>>>> >>>> > >> > +VM_BIND/UNBIND ioctl will immediately start
> > >>>>>>>>> >>>> binding/unbinding
> > >>>>>>>>> >>>> > the mapping in an
> > >>>>>>>>> >>>> > >> > +async worker. The binding and
> > >>>>>>>>>unbinding will
> > >>>>>>>>> >>>>work like a
> > >>>>>>>>> >>>> special
> > >>>>>>>>> >>>> > GPU engine.
> > >>>>>>>>> >>>> > >> > +The binding and unbinding operations are
> > >>>>>>>>> serialized and
> > >>>>>>>>> >>>> will
> > >>>>>>>>> >>>> > wait on specified
> > >>>>>>>>> >>>> > >> > +input fences before the operation
> > >>>>>>>>>and will signal
> > >>>>>>>>> the
> > >>>>>>>>> >>>> output
> > >>>>>>>>> >>>> > fences upon the
> > >>>>>>>>> >>>> > >> > +completion of the operation. Due to
> > >>>>>>>>> serialization,
> > >>>>>>>>> >>>> completion of
> > >>>>>>>>> >>>> > an operation
> > >>>>>>>>> >>>> > >> > +will also indicate that all
> > >>>>>>>>>previous operations
> > >>>>>>>>> >>>>are also
> > >>>>>>>>> >>>> > complete.
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >> I guess we should avoid saying "will
> > >>>>>>>>>immediately
> > >>>>>>>>> start
> > >>>>>>>>> >>>> > binding/unbinding" if
> > >>>>>>>>> >>>> > >> there are fences involved.
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >> And the fact that it's happening in an async
> > >>>>>>>>> >>>>worker seem to
> > >>>>>>>>> >>>> imply
> > >>>>>>>>> >>>> > it's not
> > >>>>>>>>> >>>> > >> immediate.
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > Ok, will fix.
> > >>>>>>>>> >>>> > This was added because in earlier design
> > >>>>>>>>>binding was
> > >>>>>>>>> deferred
> > >>>>>>>>> >>>> until
> > >>>>>>>>> >>>> > next execbuff.
> > >>>>>>>>> >>>> > But now it is non-deferred (immediate in
> > >>>>>>>>>that sense).
> > >>>>>>>>> >>>>But yah,
> > >>>>>>>>> >>>> this is
> > >>>>>>>>> >>>> > confusing
> > >>>>>>>>> >>>> > and will fix it.
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >> I have a question on the behavior of the bind
> > >>>>>>>>> >>>>operation when
> > >>>>>>>>> >>>> no
> > >>>>>>>>> >>>> > input fence
> > >>>>>>>>> >>>> > >> is provided. Let say I do :
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >> VM_BIND (out_fence=fence1)
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >> VM_BIND (out_fence=fence2)
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >> VM_BIND (out_fence=fence3)
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >> In what order are the fences going to
> > >>>>>>>>>be signaled?
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >> In the order of VM_BIND ioctls? Or out
> > >>>>>>>>>of order?
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >> Because you wrote "serialized I assume
> > >>>>>>>>>it's : in
> > >>>>>>>>> order
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > Yes, in the order of VM_BIND/UNBIND
> > >>>>>>>>>ioctls. Note that
> > >>>>>>>>> >>>>bind and
> > >>>>>>>>> >>>> unbind
> > >>>>>>>>> >>>> > will use
> > >>>>>>>>> >>>> > the same queue and hence are ordered.
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >> One thing I didn't realize is that
> > >>>>>>>>>because we only
> > >>>>>>>>> get one
> > >>>>>>>>> >>>> > "VM_BIND" engine,
> > >>>>>>>>> >>>> > >> there is a disconnect from the Vulkan
> > >>>>>>>>>specification.
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >> In Vulkan VM_BIND operations are
> > >>>>>>>>>serialized but
> > >>>>>>>>> >>>>per engine.
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >> So you could have something like this :
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >> VM_BIND (engine=rcs0, in_fence=fence1,
> > >>>>>>>>> out_fence=fence2)
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >> VM_BIND (engine=ccs0, in_fence=fence3,
> > >>>>>>>>> out_fence=fence4)
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >> fence1 is not signaled
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >> fence3 is signaled
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >> So the second VM_BIND will proceed before the
> > >>>>>>>>> >>>>first VM_BIND.
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >> I guess we can deal with that scenario in
> > >>>>>>>>> >>>>userspace by doing
> > >>>>>>>>> >>>> the
> > >>>>>>>>> >>>> > wait
> > >>>>>>>>> >>>> > >> ourselves in one thread per engines.
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >> But then it makes the VM_BIND input
> > >>>>>>>>>fences useless.
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >> Daniel : what do you think? Should be
> > >>>>>>>>>rework this or
> > >>>>>>>>> just
> > >>>>>>>>> >>>> deal with
> > >>>>>>>>> >>>> > wait
> > >>>>>>>>> >>>> > >> fences in userspace?
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >
> > >>>>>>>>> >>>> > >My opinion is rework this but make the
> > >>>>>>>>>ordering via
> > >>>>>>>>> >>>>an engine
> > >>>>>>>>> >>>> param
> > >>>>>>>>> >>>> > optional.
> > >>>>>>>>> >>>> > >
> > >>>>>>>>> >>>> > >e.g. A VM can be configured so all binds
> > >>>>>>>>>are ordered
> > >>>>>>>>> >>>>within the
> > >>>>>>>>> >>>> VM
> > >>>>>>>>> >>>> > >
> > >>>>>>>>> >>>> > >e.g. A VM can be configured so all binds
> > >>>>>>>>>accept an
> > >>>>>>>>> engine
> > >>>>>>>>> >>>> argument
> > >>>>>>>>> >>>> > (in
> > >>>>>>>>> >>>> > >the case of the i915 likely this is a
> > >>>>>>>>>gem context
> > >>>>>>>>> >>>>handle) and
> > >>>>>>>>> >>>> binds
> > >>>>>>>>> >>>> > >ordered with respect to that engine.
> > >>>>>>>>> >>>> > >
> > >>>>>>>>> >>>> > >This gives UMDs options as the later
> > >>>>>>>>>likely consumes
> > >>>>>>>>> >>>>more KMD
> > >>>>>>>>> >>>> > resources
> > >>>>>>>>> >>>> > >so if a different UMD can live with
> > >>>>binds being
> > >>>>>>>>> >>>>ordered within
> > >>>>>>>>> >>>> the VM
> > >>>>>>>>> >>>> > >they can use a mode consuming less resources.
> > >>>>>>>>> >>>> > >
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > I think we need to be careful here if we
> > >>>>>>>>>are looking
> > >>>>>>>>> for some
> > >>>>>>>>> >>>> out of
> > >>>>>>>>> >>>> > (submission) order completion of vm_bind/unbind.
> > >>>>>>>>> >>>> > In-order completion means, in a batch of
> > >>>>>>>>>binds and
> > >>>>>>>>> >>>>unbinds to be
> > >>>>>>>>> >>>> > completed in-order, user only needs to specify
> > >>>>>>>>> >>>>in-fence for the
> > >>>>>>>>> >>>> > first bind/unbind call and the our-fence
> > >>>>>>>>>for the last
> > >>>>>>>>> >>>> bind/unbind
> > >>>>>>>>> >>>> > call. Also, the VA released by an unbind
> > >>>>>>>>>call can be
> > >>>>>>>>> >>>>re-used by
> > >>>>>>>>> >>>> > any subsequent bind call in that
> > >>>>in-order batch.
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > These things will break if
> > >>>>>>>>>binding/unbinding were to
> > >>>>>>>>> >>>>be allowed
> > >>>>>>>>> >>>> to
> > >>>>>>>>> >>>> > go out of order (of submission) and user
> > >>>>>>>>>need to be
> > >>>>>>>>> extra
> > >>>>>>>>> >>>> careful
> > >>>>>>>>> >>>> > not to run into pre-mature triggereing of
> > >>>>>>>>>out-fence and
> > >>>>>>>>> bind
> > >>>>>>>>> >>>> failing
> > >>>>>>>>> >>>> > as VA is still in use etc.
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > Also, VM_BIND binds the provided
> > >>>>mapping on the
> > >>>>>>>>> specified
> > >>>>>>>>> >>>> address
> > >>>>>>>>> >>>> > space
> > >>>>>>>>> >>>> > (VM). So, the uapi is not engine/context
> > >>>>>>>>>specific.
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > We can however add a 'queue' to the uapi
> > >>>>>>>>>which can be
> > >>>>>>>>> >>>>one from
> > >>>>>>>>> >>>> the
> > >>>>>>>>> >>>> > pre-defined queues,
> > >>>>>>>>> >>>> > I915_VM_BIND_QUEUE_0
> > >>>>>>>>> >>>> > I915_VM_BIND_QUEUE_1
> > >>>>>>>>> >>>> > ...
> > >>>>>>>>> >>>> > I915_VM_BIND_QUEUE_(N-1)
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > KMD will spawn an async work queue for
> > >>>>>>>>>each queue which
> > >>>>>>>>> will
> > >>>>>>>>> >>>> only
> > >>>>>>>>> >>>> > bind the mappings on that queue in the
> > >>>>order of
> > >>>>>>>>> submission.
> > >>>>>>>>> >>>> > User can assign the queue to per engine
> > >>>>>>>>>or anything
> > >>>>>>>>> >>>>like that.
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > But again here, user need to be
> > >>>>careful and not
> > >>>>>>>>> >>>>deadlock these
> > >>>>>>>>> >>>> > queues with circular dependency of fences.
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > I prefer adding this later an as
> > >>>>>>>>>extension based on
> > >>>>>>>>> >>>>whether it
> > >>>>>>>>> >>>> > is really helping with the implementation.
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > I can tell you right now that having
> > >>>>>>>>>everything on a
> > >>>>>>>>> single
> > >>>>>>>>> >>>> in-order
> > >>>>>>>>> >>>> > queue will not get us the perf we want.
> > >>>>>>>>>What vulkan
> > >>>>>>>>> >>>>really wants
> > >>>>>>>>> >>>> is one
> > >>>>>>>>> >>>> > of two things:
> > >>>>>>>>> >>>> > 1. No implicit ordering of VM_BIND
> > >>>>ops. They just
> > >>>>>>>>> happen in
> > >>>>>>>>> >>>> whatever
> > >>>>>>>>> >>>> > their dependencies are resolved and we
> > >>>>>>>>>ensure ordering
> > >>>>>>>>> >>>>ourselves
> > >>>>>>>>> >>>> by
> > >>>>>>>>> >>>> > having a syncobj in the VkQueue.
> > >>>>>>>>> >>>> > 2. The ability to create multiple VM_BIND
> > >>>>>>>>>queues. We
> > >>>>>>>>> need at
> > >>>>>>>>> >>>> least 2
> > >>>>>>>>> >>>> > but I don't see why there needs to be a
> > >>>>>>>>>limit besides
> > >>>>>>>>> >>>>the limits
> > >>>>>>>>> >>>> the
> > >>>>>>>>> >>>> > i915 API already has on the number of
> > >>>>>>>>>engines. Vulkan
> > >>>>>>>>> could
> > >>>>>>>>> >>>> expose
> > >>>>>>>>> >>>> > multiple sparse binding queues to the
> > >>>>>>>>>client if it's not
> > >>>>>>>>> >>>> arbitrarily
> > >>>>>>>>> >>>> > limited.
> > >>>>>>>>> >>>>
> > >>>>>>>>> >>>> Thanks Jason, Lionel.
> > >>>>>>>>> >>>>
> > >>>>>>>>> >>>> Jason, what are you referring to when you say
> > >>>>>>>>>"limits the i915
> > >>>>>>>>> API
> > >>>>>>>>> >>>> already
> > >>>>>>>>> >>>> has on the number of engines"? I am not sure if
> > >>>>>>>>>there is such
> > >>>>>>>>> an uapi
> > >>>>>>>>> >>>> today.
> > >>>>>>>>> >>>>
> > >>>>>>>>> >>>> There's a limit of something like 64 total engines
> > >>>>>>>>>today based on
> > >>>>>>>>> the
> > >>>>>>>>> >>>> number of bits we can cram into the exec flags in
> > >>>>>>>>>execbuffer2. I
> > >>>>>>>>> think
> > >>>>>>>>> >>>> someone had an extended version that allowed more
> > >>>>>>>>>but I ripped it
> > >>>>>>>>> out
> > >>>>>>>>> >>>> because no one was using it. Of course,
> > >>>>>>>>>execbuffer3 might not
> > >>>>>>>>> >>>>have that
> > >>>>>>>>> >>>> problem at all.
> > >>>>>>>>> >>>>
> > >>>>>>>>> >>>
> > >>>>>>>>> >>>Thanks Jason.
> > >>>>>>>>> >>>Ok, I am not sure which exec flag is that, but yah,
> > >>>>>>>>>execbuffer3
> > >>>>>>>>> probably
> > >>>>>>>>> >>>will not have this limiation. So, we need to define a
> > >>>>>>>>> VM_BIND_MAX_QUEUE
> > >>>>>>>>> >>>and somehow export it to user (I am thinking of
> > >>>>>>>>>embedding it in
> > >>>>>>>>> >>>I915_PARAM_HAS_VM_BIND. bits[0]->HAS_VM_BIND,
> > >>>>bits[1-3]->'n'
> > >>>>>>>>> meaning 2^n
> > >>>>>>>>> >>>queues.
> > >>>>>>>>> >>
> > >>>>>>>>> >>Ah, I think you are waking about I915_EXEC_RING_MASK
> > >>>>>>>>>(0x3f) which
> > >>>>>>>>> execbuf3
> > >>>>>>>>>
> > >>>>>>>>> Yup! That's exactly the limit I was talking about.
> > >>>>>>>>>
> > >>>>>>>>> >>will also have. So, we can simply define in
> vm_bind/unbind
> > >>>>>>>>> structures,
> > >>>>>>>>> >>
> > >>>>>>>>> >>#define I915_VM_BIND_MAX_QUEUE 64
> > >>>>>>>>> >> __u32 queue;
> > >>>>>>>>> >>
> > >>>>>>>>> >>I think that will keep things simple.
> > >>>>>>>>> >
> > >>>>>>>>> >Hmmm? What does execbuf2 limit has to do with how
> > >>>>many engines
> > >>>>>>>>> >hardware can have? I suggest not to do that.
> > >>>>>>>>> >
> > >>>>>>>>> >Change with added this:
> > >>>>>>>>> >
> > >>>>>>>>> > if (set.num_engines > I915_EXEC_RING_MASK + 1)
> > >>>>>>>>> > return -EINVAL;
> > >>>>>>>>> >
> > >>>>>>>>> >To context creation needs to be undone and so let users
> > >>>>>>>>>create engine
> > >>>>>>>>> >maps with all hardware engines, and let execbuf3 access
> > >>>>>>>>>them all.
> > >>>>>>>>> >
> > >>>>>>>>>
> > >>>>>>>>> Earlier plan was to carry I915_EXEC_RING_MAP (0x3f) to
> > >>>>>>>>>execbuff3 also.
> > >>>>>>>>> Hence, I was using the same limit for VM_BIND queues
> > >>>>>>>>>(64, or 65 if we
> > >>>>>>>>> make it N+1).
> > >>>>>>>>> But, as discussed in other thread of this RFC series, we
> > >>>>>>>>>are planning
> > >>>>>>>>> to drop this I915_EXEC_RING_MAP in execbuff3. So,
> > >>>>there won't be
> > >>>>>>>>> any uapi that limits the number of engines (and hence
> > >>>>>>>>>the vm_bind
> > >>>>>>>>> queues
> > >>>>>>>>> need to be supported).
> > >>>>>>>>>
> > >>>>>>>>> If we leave the number of vm_bind queues to be
> > >>>>arbitrarily large
> > >>>>>>>>> (__u32 queue_idx) then, we need to have a hashmap for
> > >>>>>>>>>queue (a wq,
> > >>>>>>>>> work_item and a linked list) lookup from the user
> > >>>>>>>>>specified queue
> > >>>>>>>>> index.
> > >>>>>>>>> Other option is to just put some hard limit (say 64 or
> > >>>>>>>>>65) and use
> > >>>>>>>>> an array of queues in VM (each created upon first use).
> > >>>>>>>>>I prefer this.
> > >>>>>>>>>
> > >>>>>>>>> I don't get why a VM_BIND queue is any different from any
> > >>>>>>>>>other queue or
> > >>>>>>>>> userspace-visible kernel object. But I'll leave those
> > >>>>>>>>>details up to
> > >>>>>>>>> danvet or whoever else might be reviewing the
> > implementation.
> > >>>>>>>>> --Jason
> > >>>>>>>>>
> > >>>>>>>>> I kind of agree here. Wouldn't be simpler to have the bind
> > >>>>>>>>>queue created
> > >>>>>>>>> like the others when we build the engine map?
> > >>>>>>>>>
> > >>>>>>>>> For userspace it's then just matter of selecting the right
> > >>>>>>>>>queue ID when
> > >>>>>>>>> submitting.
> > >>>>>>>>>
> > >>>>>>>>> If there is ever a possibility to have this work on the GPU,
> > >>>>>>>>>it would be
> > >>>>>>>>> all ready.
> > >>>>>>>>>
> > >>>>>>>>
> > >>>>>>>>I did sync offline with Matt Brost on this.
> > >>>>>>>>We can add a VM_BIND engine class and let user create
> VM_BIND
> > >>>>>>>>engines (queues).
> > >>>>>>>>The problem is, in i915 engine creating interface is bound to
> > >>>>>>>>gem_context.
> > >>>>>>>>So, in vm_bind ioctl, we would need both context_id and
> > >>>>>>>>queue_idx for proper
> > >>>>>>>>lookup of the user created engine. This is bit ackward as
> > >>>>vm_bind is an
> > >>>>>>>>interface to VM (address space) and has nothing to do with
> > >>>>gem_context.
> > >>>>>>>
> > >>>>>>>
> > >>>>>>>A gem_context has a single vm object right?
> > >>>>>>>
> > >>>>>>>Set through I915_CONTEXT_PARAM_VM at creation or given a
> > default
> > >>>>>>>one if not.
> > >>>>>>>
> > >>>>>>>So it's just like picking up the vm like it's done at execbuffer
> > >>>>>>>time right now : eb->context->vm
> > >>>>>>>
> > >>>>>>
> > >>>>>>Are you suggesting replacing 'vm_id' with 'context_id' in the
> > >>>>>>VM_BIND/UNBIND
> > >>>>>>ioctl and probably call it CONTEXT_BIND/UNBIND, because VM can
> > be
> > >>>>>>obtained
> > >>>>>>from the context?
> > >>>>>
> > >>>>>
> > >>>>>Yes, because if we go for engines, they're associated with a context
> > >>>>>and so also associated with the VM bound to the context.
> > >>>>>
> > >>>>
> > >>>>Hmm...context doesn't sould like the right interface. It should be
> > >>>>VM and engine (independent of context). Engine can be virtual or soft
> > >>>>engine (kernel thread), each with its own queue. We can add an
> > >>>>interface
> > >>>>to create such engines (independent of context). But we are anway
> > >>>>implicitly creating it when user uses a new queue_idx. If in future
> > >>>>we have hardware engines for VM_BIND operation, we can have that
> > >>>>explicit inteface to create engine instances and the queue_index
> > >>>>in vm_bind/unbind will point to those engines.
> > >>>>Anyone has any thoughts? Daniel?
> > >>>
> > >>>Exposing gem_context or intel_context to user space is a strange
> > >>>concept to me. A context represent some hw resources that is used
> > >>>to complete certain task. User space should care allocate some
> > >>>resources (memory, queues) and submit tasks to queues. But user
> > >>>space doesn't care how certain task is mapped to a HW context -
> > >>>driver/guc should take care of this.
> > >>>
> > >>>So a cleaner interface to me is: user space create a vm, create
> > >>>gem object, vm_bind it to a vm; allocate queues (internally
> > >>>represent compute or blitter HW. Queue can be virtual to user) for
> > >>>this vm; submit tasks to queues. User can create multiple queues
> > >>>under one vm. One queue is only for one vm.
> > >>>
> > >>>I915 driver/guc manage the hw compute or blitter resources which
> > >>>is transparent to user space. When i915 or guc decide to schedule
> > >>>a queue (run tasks on that queue), a HW engine will be pick up and
> > >>>set up properly for the vm of that queue (ie., switch to page
> > >>>tables of that vm) - this is a context switch.
> > >>>
> > >>>From vm_bind perspective, it simply bind a gem_object to a vm.
> > >>>Engine/queue is not a parameter to vm_bind, as any engine can be
> > >>>pick up by i915/guc to execute a task using the vm bound va.
> > >>>
> > >>>I didn't completely follow the discussion here. Just share some
> > >>>thoughts.
> > >>>
> > >>
> > >>Yah, I agree.
> > >>
> > >>Lionel,
> > >>How about we define the queue as
> > >>union {
> > >> __u32 queue_idx;
> > >> __u64 rsvd;
> > >>}
> > >>
> > >>If required, we can extend by expanding the 'rsvd' field to <ctx_id,
> > >>queue_idx> later
> > >>with a flag.
> > >>
> > >>Niranjana
> > >
> > >
> > >I did not really understand Oak's comment nor what you're suggesting
> > >here to be honest.
> > >
> > >
> > >First the GEM context is already exposed to userspace. It's explicitly
> > >created by userpace with DRM_IOCTL_I915_GEM_CONTEXT_CREATE.
> > >
> > >We give the GEM context id in every execbuffer we do with
> > >drm_i915_gem_execbuffer2::rsvd1.
> > >
> > >It's still in the new execbuffer3 proposal being discussed.
> > >
> > >
> > >Second, the GEM context is also where we set the VM with
> > >I915_CONTEXT_PARAM_VM.
> > >
> > >
> > >Third, the GEM context also has the list of engines with
> > >I915_CONTEXT_PARAM_ENGINES.
> > >
> >
> > Yes, the execbuf and engine map creation are tied to gem_context.
> > (which probably is not the best interface.)
> >
> > >
> > >So it makes sense to me to dispatch the vm_bind operation to a GEM
> > >context, to a given vm_bind queue, because it's got all the
> > >information required :
> > >
> > > - the list of new vm_bind queues
> > >
> > > - the vm that is going to be modified
> > >
> >
> > But the operation is performed here on the address space (VM) which
> > can have multiple gem_contexts referring to it. So, VM is the right
> > interface here. We need not 'gem_context'ify it.
> >
> > All we need is multiple queue support for the address space (VM).
> > Going to gem_context for that just because we have engine creation
> > support there seems unnecessay and not correct to me.
> >
> > >
> > >Otherwise where do the vm_bind queues live?
> > >
> > >In the i915/drm fd object?
> > >
> > >That would mean that all the GEM contexts are sharing the same vm_bind
> > >queues.
> > >
> >
> > Not all, only the gem contexts that are using the same address space (VM).
> > But to me the right way to describe would be that "VM will be using those
> > queues".
>
>
> I hope by "queue" here you mean a HW resource that will be later used to
> execute the job, for example a ccs compute engine. Of course queue can be
> virtual so user can create more queues than what hw physically has.
>
> To express the concept of "VM will be using those queues", I think it make
> sense to have create_queue(vm) function taking a vm parameter. This
> means this queue is created for the purpose of submit job under this VM.
> Later on, we can submit job (referring to objects vm_bound to the same vm)
> to the queue. The vm_bind ioctl doesn’t need to have queue parameter, just
> vm_bind (object, va, vm).
>
> I hope the "queue" here is not the engine used to perform the vm_bind
> operation itself. But if you meant a queue/engine to perform vm_bind itself
> (vs a queue/engine for later job submission), then we can discuss more. I
> know xe driver have similar concept and I think align the design early can
> benefit the migration to xe driver.
Oops, I read more on this thread and it turned out the vm_bind queue here is actually used to perform vm bind/unbind operations. XE driver has the similar concept (except it is called engine_id there). So having a queue_idx parameter is closer to xe design.
That said, I still feel having a queue_idx parameter to vm_bind is a bit awkward. Vm_bind can be performed without any GPU engines, ie,. CPU itself can complete a vm bind as long as CPU have access to gpu's local memory. So the queue here have to be a virtual concept - it doesn't have a hard map to GPU blitter engine.
Can someone summarize what is the benefit of the queue-idx parameter? For the purpose of ordering vm_bind and later gpu jobs?
>
> Regards,
> Oak
>
> >
> > Niranjana
> >
> > >
> > >intel_context or GuC are internal details we're not concerned about.
> > >
> > >I don't really see the connection with the GEM context.
> > >
> > >
> > >Maybe Oak has a different use case than Vulkan.
> > >
> > >
> > >-Lionel
> > >
> > >
> > >>
> > >>>Regards,
> > >>>Oak
> > >>>
> > >>>>
> > >>>>Niranjana
> > >>>>
> > >>>>>
> > >>>>>>I think the interface is clean as a interface to VM. It is
> > >>>>only that we
> > >>>>>>don't have a clean way to create a raw VM_BIND engine (not
> > >>>>>>associated with
> > >>>>>>any context) with i915 uapi.
> > >>>>>>May be we can add such an interface, but I don't think that is
> > >>>>worth it
> > >>>>>>(we might as well just use a queue_idx in VM_BIND/UNBIND ioctl
> as I
> > >>>>>>mentioned
> > >>>>>>above).
> > >>>>>>Anyone has any thoughts?
> > >>>>>>
> > >>>>>>>
> > >>>>>>>>Another problem is, if two VMs are binding with the same
> defined
> > >>>>>>>>engine,
> > >>>>>>>>binding on VM1 can get unnecessary blocked by binding on VM2
> > >>>>>>>>(which may be
> > >>>>>>>>waiting on its in_fence).
> > >>>>>>>
> > >>>>>>>
> > >>>>>>>Maybe I'm missing something, but how can you have 2 vm objects
> > >>>>>>>with a single gem_context right now?
> > >>>>>>>
> > >>>>>>
> > >>>>>>No, we don't have 2 VMs for a gem_context.
> > >>>>>>Say if ctx1 with vm1 and ctx2 with vm2.
> > >>>>>>First vm_bind call was for vm1 with q_idx 1 in ctx1 engine map.
> > >>>>>>Second vm_bind call was for vm2 with q_idx 2 in ctx2 engine map. If
> > >>>>>>those two queue indicies points to same underlying vm_bind
> engine,
> > >>>>>>then the second vm_bind call gets blocked until the first
> > >>>>vm_bind call's
> > >>>>>>'in' fence is triggered and bind completes.
> > >>>>>>
> > >>>>>>With per VM queues, this is not a problem as two VMs will not
> endup
> > >>>>>>sharing same queue.
> > >>>>>>
> > >>>>>>BTW, I just posted a updated PATCH series.
> > >>>>>>https://www.spinics.net/lists/dri-devel/msg350483.html
> > >>>>>>
> > >>>>>>Niranjana
> > >>>>>>
> > >>>>>>>
> > >>>>>>>>
> > >>>>>>>>So, my preference here is to just add a 'u32 queue' index in
> > >>>>>>>>vm_bind/unbind
> > >>>>>>>>ioctl, and the queues are per VM.
> > >>>>>>>>
> > >>>>>>>>Niranjana
> > >>>>>>>>
> > >>>>>>>>> Thanks,
> > >>>>>>>>>
> > >>>>>>>>> -Lionel
> > >>>>>>>>>
> > >>>>>>>>>
> > >>>>>>>>> Niranjana
> > >>>>>>>>>
> > >>>>>>>>> >Regards,
> > >>>>>>>>> >
> > >>>>>>>>> >Tvrtko
> > >>>>>>>>> >
> > >>>>>>>>> >>
> > >>>>>>>>> >>Niranjana
> > >>>>>>>>> >>
> > >>>>>>>>> >>>
> > >>>>>>>>> >>>> I am trying to see how many queues we need and
> > >>>>>>>>>don't want it to
> > >>>>>>>>> be
> > >>>>>>>>> >>>> arbitrarily
> > >>>>>>>>> >>>> large and unduely blow up memory usage and
> > >>>>>>>>>complexity in i915
> > >>>>>>>>> driver.
> > >>>>>>>>> >>>>
> > >>>>>>>>> >>>> I expect a Vulkan driver to use at most 2 in the
> > >>>>>>>>>vast majority
> > >>>>>>>>> >>>>of cases. I
> > >>>>>>>>> >>>> could imagine a client wanting to create more
> > >>>>than 1 sparse
> > >>>>>>>>> >>>>queue in which
> > >>>>>>>>> >>>> case, it'll be N+1 but that's unlikely. As far as
> > >>>>>>>>>complexity
> > >>>>>>>>> >>>>goes, once
> > >>>>>>>>> >>>> you allow two, I don't think the complexity is
> > >>>>going up by
> > >>>>>>>>> >>>>allowing N. As
> > >>>>>>>>> >>>> for memory usage, creating more queues means more
> > >>>>>>>>>memory. That's
> > >>>>>>>>> a
> > >>>>>>>>> >>>> trade-off that userspace can make. Again, the
> > >>>>>>>>>expected number
> > >>>>>>>>> >>>>here is 1
> > >>>>>>>>> >>>> or 2 in the vast majority of cases so I don't think
> > >>>>>>>>>you need to
> > >>>>>>>>> worry.
> > >>>>>>>>> >>>
> > >>>>>>>>> >>>Ok, will start with n=3 meaning 8 queues.
> > >>>>>>>>> >>>That would require us create 8 workqueues.
> > >>>>>>>>> >>>We can change 'n' later if required.
> > >>>>>>>>> >>>
> > >>>>>>>>> >>>Niranjana
> > >>>>>>>>> >>>
> > >>>>>>>>> >>>>
> > >>>>>>>>> >>>> > Why? Because Vulkan has two basic kind of bind
> > >>>>>>>>> >>>>operations and we
> > >>>>>>>>> >>>> don't
> > >>>>>>>>> >>>> > want any dependencies between them:
> > >>>>>>>>> >>>> > 1. Immediate. These happen right after BO
> > >>>>>>>>>creation or
> > >>>>>>>>> >>>>maybe as
> > >>>>>>>>> >>>> part of
> > >>>>>>>>> >>>> > vkBindImageMemory() or
> > VkBindBufferMemory(). These
> > >>>>>>>>> >>>>don't happen
> > >>>>>>>>> >>>> on a
> > >>>>>>>>> >>>> > queue and we don't want them serialized
> > >>>>>>>>>with anything. To
> > >>>>>>>>> >>>> synchronize
> > >>>>>>>>> >>>> > with submit, we'll have a syncobj in the
> > >>>>>>>>>VkDevice which
> > >>>>>>>>> is
> > >>>>>>>>> >>>> signaled by
> > >>>>>>>>> >>>> > all immediate bind operations and make
> > >>>>>>>>>submits wait on
> > >>>>>>>>> it.
> > >>>>>>>>> >>>> > 2. Queued (sparse): These happen on a
> > >>>>>>>>>VkQueue which may
> > >>>>>>>>> be the
> > >>>>>>>>> >>>> same as
> > >>>>>>>>> >>>> > a render/compute queue or may be its own
> > >>>>>>>>>queue. It's up
> > >>>>>>>>> to us
> > >>>>>>>>> >>>> what we
> > >>>>>>>>> >>>> > want to advertise. From the Vulkan API
> > >>>>>>>>>PoV, this is like
> > >>>>>>>>> any
> > >>>>>>>>> >>>> other
> > >>>>>>>>> >>>> > queue. Operations on it wait on and signal
> > >>>>>>>>>semaphores. If we
> > >>>>>>>>> >>>> have a
> > >>>>>>>>> >>>> > VM_BIND engine, we'd provide syncobjs to
> > >>>>wait and
> > >>>>>>>>> >>>>signal just like
> > >>>>>>>>> >>>> we do
> > >>>>>>>>> >>>> > in execbuf().
> > >>>>>>>>> >>>> > The important thing is that we don't want
> > >>>>>>>>>one type of
> > >>>>>>>>> >>>>operation to
> > >>>>>>>>> >>>> block
> > >>>>>>>>> >>>> > on the other. If immediate binds are
> > >>>>>>>>>blocking on sparse
> > >>>>>>>>> binds,
> > >>>>>>>>> >>>> it's
> > >>>>>>>>> >>>> > going to cause over-synchronization issues.
> > >>>>>>>>> >>>> > In terms of the internal implementation, I
> > >>>>>>>>>know that
> > >>>>>>>>> >>>>there's going
> > >>>>>>>>> >>>> to be
> > >>>>>>>>> >>>> > a lock on the VM and that we can't actually
> > >>>>>>>>>do these
> > >>>>>>>>> things in
> > >>>>>>>>> >>>> > parallel. That's fine. Once the dma_fences have
> > >>>>>>>>> signaled and
> > >>>>>>>>> >>>> we're
> > >>>>>>>>> >>>>
> > >>>>>>>>> >>>> Thats correct. It is like a single VM_BIND
> > >>>>engine with
> > >>>>>>>>> >>>>multiple queues
> > >>>>>>>>> >>>> feeding to it.
> > >>>>>>>>> >>>>
> > >>>>>>>>> >>>> Right. As long as the queues themselves are
> > >>>>>>>>>independent and
> > >>>>>>>>> >>>>can block on
> > >>>>>>>>> >>>> dma_fences without holding up other queues, I think
> > >>>>>>>>>we're fine.
> > >>>>>>>>> >>>>
> > >>>>>>>>> >>>> > unblocked to do the bind operation, I don't care if
> > >>>>>>>>> >>>>there's a bit
> > >>>>>>>>> >>>> of
> > >>>>>>>>> >>>> > synchronization due to locking. That's
> > >>>>>>>>>expected. What
> > >>>>>>>>> >>>>we can't
> > >>>>>>>>> >>>> afford
> > >>>>>>>>> >>>> > to have is an immediate bind operation
> > >>>>>>>>>suddenly blocking
> > >>>>>>>>> on a
> > >>>>>>>>> >>>> sparse
> > >>>>>>>>> >>>> > operation which is blocked on a compute job
> > >>>>>>>>>that's going
> > >>>>>>>>> to run
> > >>>>>>>>> >>>> for
> > >>>>>>>>> >>>> > another 5ms.
> > >>>>>>>>> >>>>
> > >>>>>>>>> >>>> As the VM_BIND queue is per VM, VM_BIND on one
> > VM
> > >>>>>>>>>doesn't block
> > >>>>>>>>> the
> > >>>>>>>>> >>>> VM_BIND
> > >>>>>>>>> >>>> on other VMs. I am not sure about usecases
> > >>>>here, but just
> > >>>>>>>>> wanted to
> > >>>>>>>>> >>>> clarify.
> > >>>>>>>>> >>>>
> > >>>>>>>>> >>>> Yes, that's what I would expect.
> > >>>>>>>>> >>>> --Jason
> > >>>>>>>>> >>>>
> > >>>>>>>>> >>>> Niranjana
> > >>>>>>>>> >>>>
> > >>>>>>>>> >>>> > For reference, Windows solves this by allowing
> > >>>>>>>>> arbitrarily many
> > >>>>>>>>> >>>> paging
> > >>>>>>>>> >>>> > queues (what they call a VM_BIND
> > >>>>>>>>>engine/queue). That
> > >>>>>>>>> >>>>design works
> > >>>>>>>>> >>>> > pretty well and solves the problems in
> > >>>>>>>>>question. >>>>Again, we could
> > >>>>>>>>> >>>> just
> > >>>>>>>>> >>>> > make everything out-of-order and require
> > >>>>>>>>>using syncobjs
> > >>>>>>>>> >>>>to order
> > >>>>>>>>> >>>> things
> > >>>>>>>>> >>>> > as userspace wants. That'd be fine too.
> > >>>>>>>>> >>>> > One more note while I'm here: danvet said
> > >>>>>>>>>something on
> > >>>>>>>>> >>>>IRC about
> > >>>>>>>>> >>>> VM_BIND
> > >>>>>>>>> >>>> > queues waiting for syncobjs to
> > >>>>>>>>>materialize. We don't
> > >>>>>>>>> really
> > >>>>>>>>> >>>> want/need
> > >>>>>>>>> >>>> > this. We already have all the machinery in
> > >>>>>>>>>userspace to
> > >>>>>>>>> handle
> > >>>>>>>>> >>>> > wait-before-signal and waiting for syncobj
> > >>>>>>>>>fences to
> > >>>>>>>>> >>>>materialize
> > >>>>>>>>> >>>> and
> > >>>>>>>>> >>>> > that machinery is on by default. It
> > >>>>would actually
> > >>>>>>>>> >>>>take MORE work
> > >>>>>>>>> >>>> in
> > >>>>>>>>> >>>> > Mesa to turn it off and take advantage of
> > >>>>>>>>>the kernel
> > >>>>>>>>> >>>>being able to
> > >>>>>>>>> >>>> wait
> > >>>>>>>>> >>>> > for syncobjs to materialize. Also, getting
> > >>>>>>>>>that right is
> > >>>>>>>>> >>>> ridiculously
> > >>>>>>>>> >>>> > hard and I really don't want to get it
> > >>>>>>>>>wrong in kernel
> > >>>>>>>>> >>>>space. �� When we
> > >>>>>>>>> >>>> > do memory fences, wait-before-signal will
> > >>>>>>>>>be a thing. We
> > >>>>>>>>> don't
> > >>>>>>>>> >>>> need to
> > >>>>>>>>> >>>> > try and make it a thing for syncobj.
> > >>>>>>>>> >>>> > --Jason
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > Thanks Jason,
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > I missed the bit in the Vulkan spec that
> > >>>>>>>>>we're allowed to
> > >>>>>>>>> have a
> > >>>>>>>>> >>>> sparse
> > >>>>>>>>> >>>> > queue that does not implement either graphics
> > >>>>>>>>>or compute
> > >>>>>>>>> >>>>operations
> > >>>>>>>>> >>>> :
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > "While some implementations may include
> > >>>>>>>>> >>>> VK_QUEUE_SPARSE_BINDING_BIT
> > >>>>>>>>> >>>> > support in queue families that also include
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > graphics and compute support, other
> > >>>>>>>>>implementations may
> > >>>>>>>>> only
> > >>>>>>>>> >>>> expose a
> > >>>>>>>>> >>>> > VK_QUEUE_SPARSE_BINDING_BIT-only queue
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > family."
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > So it can all be all a vm_bind engine that
> > >>>>just does
> > >>>>>>>>> bind/unbind
> > >>>>>>>>> >>>> > operations.
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > But yes we need another engine for the
> > >>>>>>>>>immediate/non-sparse
> > >>>>>>>>> >>>> operations.
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > -Lionel
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > >
> > >>>>>>>>> >>>> > Daniel, any thoughts?
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > Niranjana
> > >>>>>>>>> >>>> >
> > >>>>>>>>> >>>> > >Matt
> > >>>>>>>>> >>>> > >
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >> Sorry I noticed this late.
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >> -Lionel
> > >>>>>>>>> >>>> > >>
> > >>>>>>>>> >>>> > >>
> > >>>>>>>
> > >>>>>>>
> > >>>>>
> > >
> > >
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