[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 19:49:56 UTC 2021
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.
" [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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