[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 20:14:00 UTC 2021
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.
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.
> 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.
-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];
>> +
>> + /**
>> + * 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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