[Intel-gfx] [PATCH 1/1] i915/query: Correlate engine and cpu timestamps with better accuracy
Lionel Landwerlin
lionel.g.landwerlin at intel.com
Wed Apr 28 21:18:35 UTC 2021
On 28/04/2021 23:45, Jason Ekstrand wrote:
> On Wed, Apr 28, 2021 at 3:14 PM Lionel Landwerlin
> <lionel.g.landwerlin at intel.com> wrote:
>> On 28/04/2021 22:54, Jason Ekstrand wrote:
>>> On Wed, Apr 28, 2021 at 2:50 PM Lionel Landwerlin
>>> <lionel.g.landwerlin at intel.com> wrote:
>>>> On 28/04/2021 22:24, Jason Ekstrand wrote:
>>>>
>>>> On Wed, Apr 28, 2021 at 3:43 AM Jani Nikula <jani.nikula at linux.intel.com> wrote:
>>>>
>>>> On Tue, 27 Apr 2021, Umesh Nerlige Ramappa <umesh.nerlige.ramappa at intel.com> wrote:
>>>>
>>>> Perf measurements rely on CPU and engine timestamps to correlate
>>>> events of interest across these time domains. Current mechanisms get
>>>> these timestamps separately and the calculated delta between these
>>>> timestamps lack enough accuracy.
>>>>
>>>> To improve the accuracy of these time measurements to within a few us,
>>>> add a query that returns the engine and cpu timestamps captured as
>>>> close to each other as possible.
>>>>
>>>> Cc: dri-devel, Jason and Daniel for review.
>>>>
>>>> Thanks!
>>>>
>>>> v2: (Tvrtko)
>>>> - document clock reference used
>>>> - return cpu timestamp always
>>>> - capture cpu time just before lower dword of cs timestamp
>>>>
>>>> v3: (Chris)
>>>> - use uncore-rpm
>>>> - use __query_cs_timestamp helper
>>>>
>>>> v4: (Lionel)
>>>> - Kernel perf subsytem allows users to specify the clock id to be used
>>>> in perf_event_open. This clock id is used by the perf subsystem to
>>>> return the appropriate cpu timestamp in perf events. Similarly, let
>>>> the user pass the clockid to this query so that cpu timestamp
>>>> corresponds to the clock id requested.
>>>>
>>>> v5: (Tvrtko)
>>>> - Use normal ktime accessors instead of fast versions
>>>> - Add more uApi documentation
>>>>
>>>> v6: (Lionel)
>>>> - Move switch out of spinlock
>>>>
>>>> v7: (Chris)
>>>> - cs_timestamp is a misnomer, use cs_cycles instead
>>>> - return the cs cycle frequency as well in the query
>>>>
>>>> v8:
>>>> - Add platform and engine specific checks
>>>>
>>>> v9: (Lionel)
>>>> - Return 2 cpu timestamps in the query - captured before and after the
>>>> register read
>>>>
>>>> v10: (Chris)
>>>> - Use local_clock() to measure time taken to read lower dword of
>>>> register and return it to user.
>>>>
>>>> v11: (Jani)
>>>> - IS_GEN deprecated. User GRAPHICS_VER instead.
>>>>
>>>> Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa at intel.com>
>>>> ---
>>>> drivers/gpu/drm/i915/i915_query.c | 145 ++++++++++++++++++++++++++++++
>>>> include/uapi/drm/i915_drm.h | 48 ++++++++++
>>>> 2 files changed, 193 insertions(+)
>>>>
>>>> diff --git a/drivers/gpu/drm/i915/i915_query.c b/drivers/gpu/drm/i915/i915_query.c
>>>> index fed337ad7b68..2594b93901ac 100644
>>>> --- a/drivers/gpu/drm/i915/i915_query.c
>>>> +++ b/drivers/gpu/drm/i915/i915_query.c
>>>> @@ -6,6 +6,8 @@
>>>>
>>>> #include <linux/nospec.h>
>>>>
>>>> +#include "gt/intel_engine_pm.h"
>>>> +#include "gt/intel_engine_user.h"
>>>> #include "i915_drv.h"
>>>> #include "i915_perf.h"
>>>> #include "i915_query.h"
>>>> @@ -90,6 +92,148 @@ static int query_topology_info(struct drm_i915_private *dev_priv,
>>>> return total_length;
>>>> }
>>>>
>>>> +typedef u64 (*__ktime_func_t)(void);
>>>> +static __ktime_func_t __clock_id_to_func(clockid_t clk_id)
>>>> +{
>>>> + /*
>>>> + * Use logic same as the perf subsystem to allow user to select the
>>>> + * reference clock id to be used for timestamps.
>>>> + */
>>>> + switch (clk_id) {
>>>> + case CLOCK_MONOTONIC:
>>>> + return &ktime_get_ns;
>>>> + case CLOCK_MONOTONIC_RAW:
>>>> + return &ktime_get_raw_ns;
>>>> + case CLOCK_REALTIME:
>>>> + return &ktime_get_real_ns;
>>>> + case CLOCK_BOOTTIME:
>>>> + return &ktime_get_boottime_ns;
>>>> + case CLOCK_TAI:
>>>> + return &ktime_get_clocktai_ns;
>>>> + default:
>>>> + return NULL;
>>>> + }
>>>> +}
>>>> +
>>>> +static inline int
>>>> +__read_timestamps(struct intel_uncore *uncore,
>>>> + i915_reg_t lower_reg,
>>>> + i915_reg_t upper_reg,
>>>> + u64 *cs_ts,
>>>> + u64 *cpu_ts,
>>>> + __ktime_func_t cpu_clock)
>>>> +{
>>>> + u32 upper, lower, old_upper, loop = 0;
>>>> +
>>>> + upper = intel_uncore_read_fw(uncore, upper_reg);
>>>> + do {
>>>> + cpu_ts[1] = local_clock();
>>>> + cpu_ts[0] = cpu_clock();
>>>> + lower = intel_uncore_read_fw(uncore, lower_reg);
>>>> + cpu_ts[1] = local_clock() - cpu_ts[1];
>>>> + old_upper = upper;
>>>> + upper = intel_uncore_read_fw(uncore, upper_reg);
>>>> + } while (upper != old_upper && loop++ < 2);
>>>> +
>>>> + *cs_ts = (u64)upper << 32 | lower;
>>>> +
>>>> + return 0;
>>>> +}
>>>> +
>>>> +static int
>>>> +__query_cs_cycles(struct intel_engine_cs *engine,
>>>> + u64 *cs_ts, u64 *cpu_ts,
>>>> + __ktime_func_t cpu_clock)
>>>> +{
>>>> + struct intel_uncore *uncore = engine->uncore;
>>>> + enum forcewake_domains fw_domains;
>>>> + u32 base = engine->mmio_base;
>>>> + intel_wakeref_t wakeref;
>>>> + int ret;
>>>> +
>>>> + fw_domains = intel_uncore_forcewake_for_reg(uncore,
>>>> + RING_TIMESTAMP(base),
>>>> + FW_REG_READ);
>>>> +
>>>> + with_intel_runtime_pm(uncore->rpm, wakeref) {
>>>> + spin_lock_irq(&uncore->lock);
>>>> + intel_uncore_forcewake_get__locked(uncore, fw_domains);
>>>> +
>>>> + ret = __read_timestamps(uncore,
>>>> + RING_TIMESTAMP(base),
>>>> + RING_TIMESTAMP_UDW(base),
>>>> + cs_ts,
>>>> + cpu_ts,
>>>> + cpu_clock);
>>>> +
>>>> + intel_uncore_forcewake_put__locked(uncore, fw_domains);
>>>> + spin_unlock_irq(&uncore->lock);
>>>> + }
>>>> +
>>>> + return ret;
>>>> +}
>>>> +
>>>> +static int
>>>> +query_cs_cycles(struct drm_i915_private *i915,
>>>> + struct drm_i915_query_item *query_item)
>>>> +{
>>>> + struct drm_i915_query_cs_cycles __user *query_ptr;
>>>> + struct drm_i915_query_cs_cycles query;
>>>> + struct intel_engine_cs *engine;
>>>> + __ktime_func_t cpu_clock;
>>>> + int ret;
>>>> +
>>>> + if (GRAPHICS_VER(i915) < 6)
>>>> + return -ENODEV;
>>>> +
>>>> + query_ptr = u64_to_user_ptr(query_item->data_ptr);
>>>> + ret = copy_query_item(&query, sizeof(query), sizeof(query), query_item);
>>>> + if (ret != 0)
>>>> + return ret;
>>>> +
>>>> + if (query.flags)
>>>> + return -EINVAL;
>>>> +
>>>> + if (query.rsvd)
>>>> + return -EINVAL;
>>>> +
>>>> + cpu_clock = __clock_id_to_func(query.clockid);
>>>> + if (!cpu_clock)
>>>> + return -EINVAL;
>>>> +
>>>> + engine = intel_engine_lookup_user(i915,
>>>> + query.engine.engine_class,
>>>> + query.engine.engine_instance);
>>>> + if (!engine)
>>>> + return -EINVAL;
>>>> +
>>>> + if (GRAPHICS_VER(i915) == 6 &&
>>>> + query.engine.engine_class != I915_ENGINE_CLASS_RENDER)
>>>> + return -ENODEV;
>>>> +
>>>> + query.cs_frequency = engine->gt->clock_frequency;
>>>> + ret = __query_cs_cycles(engine,
>>>> + &query.cs_cycles,
>>>> + query.cpu_timestamp,
>>>> + cpu_clock);
>>>> + if (ret)
>>>> + return ret;
>>>> +
>>>> + if (put_user(query.cs_frequency, &query_ptr->cs_frequency))
>>>> + return -EFAULT;
>>>> +
>>>> + if (put_user(query.cpu_timestamp[0], &query_ptr->cpu_timestamp[0]))
>>>> + return -EFAULT;
>>>> +
>>>> + if (put_user(query.cpu_timestamp[1], &query_ptr->cpu_timestamp[1]))
>>>> + return -EFAULT;
>>>> +
>>>> + if (put_user(query.cs_cycles, &query_ptr->cs_cycles))
>>>> + return -EFAULT;
>>>> +
>>>> + return sizeof(query);
>>>> +}
>>>> +
>>>> static int
>>>> query_engine_info(struct drm_i915_private *i915,
>>>> struct drm_i915_query_item *query_item)
>>>> @@ -424,6 +568,7 @@ static int (* const i915_query_funcs[])(struct drm_i915_private *dev_priv,
>>>> query_topology_info,
>>>> query_engine_info,
>>>> query_perf_config,
>>>> + query_cs_cycles,
>>>> };
>>>>
>>>> int i915_query_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
>>>> diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
>>>> index 6a34243a7646..08b00f1709b5 100644
>>>> --- a/include/uapi/drm/i915_drm.h
>>>> +++ b/include/uapi/drm/i915_drm.h
>>>> @@ -2230,6 +2230,10 @@ struct drm_i915_query_item {
>>>> #define DRM_I915_QUERY_TOPOLOGY_INFO 1
>>>> #define DRM_I915_QUERY_ENGINE_INFO 2
>>>> #define DRM_I915_QUERY_PERF_CONFIG 3
>>>> + /**
>>>> + * Query Command Streamer timestamp register.
>>>> + */
>>>> +#define DRM_I915_QUERY_CS_CYCLES 4
>>>> /* Must be kept compact -- no holes and well documented */
>>>>
>>>> /**
>>>> @@ -2397,6 +2401,50 @@ struct drm_i915_engine_info {
>>>> __u64 rsvd1[4];
>>>> };
>>>>
>>>> +/**
>>>> + * struct drm_i915_query_cs_cycles
>>>> + *
>>>> + * The query returns the command streamer cycles and the frequency that can be
>>>> + * used to calculate the command streamer timestamp. In addition the query
>>>> + * returns a set of cpu timestamps that indicate when the command streamer cycle
>>>> + * count was captured.
>>>> + */
>>>> +struct drm_i915_query_cs_cycles {
>>>> + /** Engine for which command streamer cycles is queried. */
>>>> + struct i915_engine_class_instance engine;
>>>>
>>>> Why is this per-engine? Do we actually expect it to change between
>>>> engines?
>>>>
>>>>
>>>> Each engine has its own timestamp register.
>>>>
>>>>
>>>> If so, we may have a problem because Vulkan expects a
>>>> unified timestamp domain for all command streamer timestamp queries.
>>>>
>>>>
>>>> I don't think it does : "
>>>>
>>>> Timestamps may only be meaningfully compared if they are written by commands submitted to the same queue.
>>> Yes but vkGetCalibratedTimestampsEXT() doesn't take a queue or even a
>>> queue family.
>>
>> I know, I brought up the issue recently. See khronos issue 2551.
> I guess this is what I get for not attending the Vulkan SI call
> anymore. Small price to pay....
>
> So the answer is that we just stop exposing the DEVICE time domain as
> soon as we start using anything other than RENDER? Seems a bit rough
> but should be doable.
>
>> You might not like the resolution... I did propose to do a rev2 of the
>> extension to let the user specify the queue.
>>
>> We can still do that in the future.
> Yeah, I think we'll want to do something if we care about this
> extension. One option would be to make it take a queue family.
> Another would be to expose it as one domain per queue family.
> Anyway... that's a discussion for another forum.
>
>>> Also, VkPhysicalDeviceLimits::timestampPeriod gives a
>>> single timestampPeriod for all queues.
>>
>> That is fine for us, we should have the same period on all command
>> streamers.
> I guess I've got no problem returning the period as part of this
> query. ANV should probably assert that it's what it expects, though.
>
>> -Lionel
>>
>>
>>> It's possible that Vulkan
>>> messed up real bad there but I thought we did a HW survey at the time
>>> and determined that it was ok.
>>>
>>> --Jason
>>>
>>>
>>>> " [1]
>>>>
>>>>
>>>> [1] : https://www.khronos.org/registry/vulkan/specs/1.2-extensions/man/html/vkCmdWriteTimestamp.html
>>>>
>>>>
>>>> -Lionel
>>>>
>>>>
>>>>
>>>> --Jason
>>>>
>>>>
>>>> + /** Must be zero. */
>>>> + __u32 flags;
>>>> +
>>>> + /**
>>>> + * Command streamer cycles as read from the command streamer
>>>> + * register at 0x358 offset.
>>>> + */
>>>> + __u64 cs_cycles;
>>>> +
>>>> + /** Frequency of the cs cycles in Hz. */
>>>> + __u64 cs_frequency;
>>>> +
>>>> + /**
>>>> + * CPU timestamps in ns. cpu_timestamp[0] is captured before reading the
>>>> + * cs_cycles register using the reference clockid set by the user.
>>>> + * cpu_timestamp[1] is the time taken in ns to read the lower dword of
>>>> + * the cs_cycles register.
>>>> + */
>>>> + __u64 cpu_timestamp[2];
> I think the API would be more clear if we had separate cpu_timestamp
> and cpu_delta fields or something like that. That or make
> cpu_timestamp[1] the end time rather than a delta. It's weird to have
> an array where the first entry is absolute and the second entry is a
> delta.
Oh dear... I did not notice that :(
I thought that was just a little dance to save local variable...
Agreed, 2 different names or 2 snapshots.
-Lionel
>
> --Jason
>
>
>>>> +
>>>> + /**
>>>> + * Reference clock id for CPU timestamp. For definition, see
>>>> + * clock_gettime(2) and perf_event_open(2). Supported clock ids are
>>>> + * CLOCK_MONOTONIC, CLOCK_MONOTONIC_RAW, CLOCK_REALTIME, CLOCK_BOOTTIME,
>>>> + * CLOCK_TAI.
>>>> + */
>>>> + __s32 clockid;
>>>> +
>>>> + /** Must be zero. */
>>>> + __u32 rsvd;
>>>> +};
>>>> +
>>>> /**
>>>> * struct drm_i915_query_engine_info
>>>> *
>>>>
>>>> --
>>>> Jani Nikula, Intel Open Source Graphics Center
>>>>
>>>>
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