[Intel-gfx] [PATCH 1/1] i915/query: Correlate engine and cpu timestamps with better accuracy
Jason Ekstrand
jason at jlekstrand.net
Thu Apr 29 19:07:58 UTC 2021
On Wed, Apr 28, 2021 at 7:34 PM 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.
>
> 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.
>
> v12: (Jason)
> - Split cpu timestamp array into timestamp and delta for cleaner API
>
> Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa at intel.com>
> Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
> ---
> drivers/gpu/drm/i915/i915_query.c | 148 ++++++++++++++++++++++++++++++
> include/uapi/drm/i915_drm.h | 52 +++++++++++
> 2 files changed, 200 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/i915_query.c b/drivers/gpu/drm/i915/i915_query.c
> index fed337ad7b68..357c44e8177c 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 +92,151 @@ 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,
> + u64 *cpu_delta,
> + __ktime_func_t cpu_clock)
> +{
> + u32 upper, lower, old_upper, loop = 0;
> +
> + upper = intel_uncore_read_fw(uncore, upper_reg);
> + do {
> + *cpu_delta = local_clock();
> + *cpu_ts = cpu_clock();
> + lower = intel_uncore_read_fw(uncore, lower_reg);
> + *cpu_delta = local_clock() - *cpu_delta;
> + 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, u64 *cpu_delta,
> + __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_delta,
> + 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,
> + &query.cpu_delta,
> + cpu_clock);
> + if (ret)
> + return ret;
> +
> + if (put_user(query.cs_frequency, &query_ptr->cs_frequency))
> + return -EFAULT;
> +
> + if (put_user(query.cpu_timestamp, &query_ptr->cpu_timestamp))
> + return -EFAULT;
> +
> + if (put_user(query.cpu_delta, &query_ptr->cpu_delta))
> + 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 +571,7 @@ 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..0b4c27092d41 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 +2401,54 @@ 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;
I've checked with HW engineers and they're claiming that all CS
timestamp registers should report the same time modulo minor drift.
You're CC'd on the internal e-mail. If this is really the case, then
I don't think we want to put an engine in this query.
--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 timestamp in ns. The timestamp is captured before reading the
> + * cs_cycles register using the reference clockid set by the user.
> + */
> + __u64 cpu_timestamp;
> +
> + /**
> + * Time delta in ns captured around reading the lower dword of the
> + * cs_cycles register.
> + */
> + __u64 cpu_delta;
> +
> + /**
> + * 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
> *
> --
> 2.20.1
>
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