Re: [Intel-gfx] [PATCH 1/1] i915/query: Correlate engine and cpu timestamps with better accuracy

[Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>]

On Fri, Apr 23, 2021 at 10:05:34AM +0300, Lionel Landwerlin wrote:
>On 21/04/2021 20:28, Umesh Nerlige Ramappa 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.
>>
>>Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@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..25b96927ab92 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 (INTEL_GEN(i915) < 6)
>>+		return -ENODEV;

Less than gen6 is handled here early on.

>>+
>>+	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 (IS_GEN(i915, 6) &&
>>+	    query.engine.engine_class != I915_ENGINE_CLASS_RENDER)
>>+		return -ENODEV;
>
>
>Thanks a bunch for rebasing this.
>
>My only comment on this patch would be : don't we want 
>IS_GEN_RANGE(i915, 1, 6) instead of IS_GEN(i915, 6) ?
>
>(assuming gen1 is a thing...)

Less than gen6 check is above at function entry. On gen6, only render 
works, so I wait until I can get the engine to check that.

Thanks,
Umesh

>
>
>-Lionel
>
>
>>+
>>+	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;
>>+
>>+	/** 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
>>   *
>
>
_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/intel-gfx