[Intel-gfx] [PATCH v3 06/12] tests/perf: rework oa-exponent test

Matthew Auld matthew.william.auld at gmail.com
Wed Aug 23 22:17:43 UTC 2017


On 08/23, Lionel Landwerlin wrote:
> New issues that were discovered while making the tests work on Gen8+ :
> 
>  - we need to measure timings between periodic reports and discard all
>    other kind of reports
> 
>  - it seems periodicity of the reports can be affected outside of RC6
>    (frequency change), we can detect this by looking at the amount of
>    clock cycles per timestamp deltas
> 
> Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
> ---
>  tests/perf.c | 734 ++++++++++++++++++++++++++++++++++++++++++++++++-----------
>  1 file changed, 600 insertions(+), 134 deletions(-)
> 
> diff --git a/tests/perf.c b/tests/perf.c
> index ca69440d..e54a14ed 100644
> --- a/tests/perf.c
> +++ b/tests/perf.c
> @@ -28,6 +28,7 @@
>  #include <fcntl.h>
>  #include <inttypes.h>
>  #include <errno.h>
> +#include <signal.h>
>  #include <sys/stat.h>
>  #include <sys/time.h>
>  #include <sys/times.h>
> @@ -306,6 +307,25 @@ static uint32_t (*read_report_ticks)(uint32_t *report,
>  static void (*sanity_check_reports)(uint32_t *oa_report0, uint32_t *oa_report1,
>  				    enum drm_i915_oa_format format);
>  
> +static bool
> +timestamp_delta_within(uint32_t delta,
> +		       uint32_t expected_delta,
> +		       uint32_t margin)
> +{
> +	return delta >= (expected_delta - margin) &&
> +	       delta <= (expected_delta + margin);
> +}
> +
> +static bool
> +double_value_within(double value,
> +		    double expected,
> +		    double percent_margin)
> +{
> +	return value >= (expected - expected * percent_margin / 100.0) &&
> +	       value <= (expected + expected * percent_margin / 100.0);
> +
> +}
> +
>  static void
>  __perf_close(int fd)
>  {
> @@ -472,6 +492,20 @@ gen8_read_report_ticks(uint32_t *report, enum drm_i915_oa_format format)
>  	return report[3];
>  }
>  
> +static void
> +gen8_read_report_clock_ratios(uint32_t *report,
> +			      uint32_t *slice_freq_mhz,
> +			      uint32_t *unslice_freq_mhz)
> +{
> +	uint32_t unslice_freq = report[0] & 0x1ff;
> +	uint32_t slice_freq_low = (report[0] >> 25) & 0x7f;
> +	uint32_t slice_freq_high = (report[0] >> 9) & 0x3;
> +	uint32_t slice_freq = slice_freq_low | (slice_freq_high << 7);
> +
> +	*slice_freq_mhz = (slice_freq * 16666) / 1000;
> +	*unslice_freq_mhz = (unslice_freq * 16666) / 1000;
> +}
> +
>  static const char *
>  gen8_read_report_reason(const uint32_t *report)
>  {
> @@ -494,29 +528,6 @@ gen8_read_report_reason(const uint32_t *report)
>  		return "unknown";
>  }
>  
> -static bool
> -oa_report_is_periodic(uint32_t oa_exponent, const uint32_t *report)
> -{
> -	if (IS_HASWELL(devid)) {
> -		/* For Haswell we don't have a documented report reason field
> -		 * (though empirically report[0] bit 10 does seem to correlate
> -		 * with a timer trigger reason) so we instead infer which
> -		 * reports are timer triggered by checking if the least
> -		 * significant bits are zero and the exponent bit is set.
> -		 */
> -		uint32_t oa_exponent_mask = (1 << (oa_exponent + 1)) - 1;
> -
> -		if ((report[1] & oa_exponent_mask) != (1 << oa_exponent))
> -			return true;
> -	} else {
> -		if ((report[0] >> OAREPORT_REASON_SHIFT) &
> -		    OAREPORT_REASON_TIMER)
> -			return true;
> -	}
> -
> -	return false;
> -}
> -
>  static uint64_t
>  timebase_scale(uint32_t u32_delta)
>  {
> @@ -563,6 +574,29 @@ oa_exponent_to_ns(int exponent)
>         return 1000000000ULL * (2ULL << exponent) / timestamp_frequency;
>  }
>  
> +static bool
> +oa_report_is_periodic(uint32_t oa_exponent, const uint32_t *report)
> +{
> +	if (IS_HASWELL(devid)) {
> +		/* For Haswell we don't have a documented report reason field
> +		 * (though empirically report[0] bit 10 does seem to correlate
> +		 * with a timer trigger reason) so we instead infer which
> +		 * reports are timer triggered by checking if the least
> +		 * significant bits are zero and the exponent bit is set.
> +		 */
> +		uint32_t oa_exponent_mask = (1 << (oa_exponent + 1)) - 1;
> +
> +		if ((report[1] & oa_exponent_mask) == (1 << oa_exponent))
> +			return true;
> +	} else {
> +		if ((report[0] >> OAREPORT_REASON_SHIFT) &
> +		    OAREPORT_REASON_TIMER)
> +			return true;
> +	}
> +
> +	return false;
> +}
> +
>  static bool
>  oa_report_ctx_is_valid(uint32_t *report)
>  {
> @@ -578,6 +612,128 @@ oa_report_ctx_is_valid(uint32_t *report)
>  	igt_assert(!"reached");
>  }
>  
> +static uint32_t
> +oa_report_get_ctx_id(uint32_t *report)
> +{
> +	if (!oa_report_ctx_is_valid(report))
> +		return 0xffffffff;
> +	return report[2];
> +}
> +
> +static double
> +oa_reports_tick_per_period(uint32_t *report0, uint32_t *report1)
> +{
> +	if (intel_gen(devid) < 8)
> +		return 0.0;
> +
> +	/* Measure the number GPU tick delta to timestamp delta. */
> +	return (double) (report1[3] - report0[3]) /
> +	       (double) (report1[1] - report0[1]);
> +}
> +
> +static void
> +scratch_buf_memset(drm_intel_bo *bo, int width, int height, uint32_t color)
> +{
> +	int ret;
> +
> +	ret = drm_intel_bo_map(bo, true /* writable */);
> +	igt_assert_eq(ret, 0);
> +
> +	for (int i = 0; i < width * height; i++)
> +		((uint32_t *)bo->virtual)[i] = color;
> +
> +	drm_intel_bo_unmap(bo);
> +}
> +
> +static void
> +scratch_buf_init(drm_intel_bufmgr *bufmgr,
> +		 struct igt_buf *buf,
> +		 int width, int height,
> +		 uint32_t color)
> +{
> +	size_t stride = width * 4;
> +	size_t size = stride * height;
> +	drm_intel_bo *bo = drm_intel_bo_alloc(bufmgr, "", size, 4096);
> +
> +	scratch_buf_memset(bo, width, height, color);
> +
> +	buf->bo = bo;
> +	buf->stride = stride;
> +	buf->tiling = I915_TILING_NONE;
> +	buf->size = size;
> +}
> +
> +static void
> +emit_report_perf_count(struct intel_batchbuffer *batch,
> +		       drm_intel_bo *dst_bo,
> +		       int dst_offset,
> +		       uint32_t report_id)
> +{
> +	if (IS_HASWELL(devid)) {
> +		BEGIN_BATCH(3, 1);
> +		OUT_BATCH(GEN6_MI_REPORT_PERF_COUNT);
> +		OUT_RELOC(dst_bo, I915_GEM_DOMAIN_INSTRUCTION, I915_GEM_DOMAIN_INSTRUCTION,
> +			  dst_offset);
> +		OUT_BATCH(report_id);
> +		ADVANCE_BATCH();
> +	} else {
> +		/* XXX: NB: n dwords arg is actually magic since it internally
> +		 * automatically accounts for larger addresses on gen >= 8...
> +		 */
> +		BEGIN_BATCH(3, 1);
> +		OUT_BATCH(GEN8_MI_REPORT_PERF_COUNT);
> +		OUT_RELOC(dst_bo, I915_GEM_DOMAIN_INSTRUCTION, I915_GEM_DOMAIN_INSTRUCTION,
> +			  dst_offset);
> +		OUT_BATCH(report_id);
> +		ADVANCE_BATCH();
> +	}
> +}
> +
> +static uint32_t
> +i915_get_one_gpu_timestamp(uint32_t *context_id)
> +{
> +	drm_intel_bufmgr *bufmgr = drm_intel_bufmgr_gem_init(drm_fd, 4096);
> +	drm_intel_context *mi_rpc_ctx = drm_intel_gem_context_create(bufmgr);
> +	drm_intel_bo *mi_rpc_bo = drm_intel_bo_alloc(bufmgr, "mi_rpc dest bo", 4096, 64);
> +	struct intel_batchbuffer *mi_rpc_batch = intel_batchbuffer_alloc(bufmgr, devid);
> +	int ret;
> +	uint32_t timestamp;
> +
> +	drm_intel_bufmgr_gem_enable_reuse(bufmgr);
> +
> +	if (context_id) {
> +		ret = drm_intel_gem_context_get_id(mi_rpc_ctx, context_id);
> +		igt_assert_eq(ret, 0);
> +	}
> +
> +	igt_assert(mi_rpc_ctx);
> +	igt_assert(mi_rpc_bo);
> +	igt_assert(mi_rpc_batch);
> +
> +	ret = drm_intel_bo_map(mi_rpc_bo, true);
> +	igt_assert_eq(ret, 0);
> +	memset(mi_rpc_bo->virtual, 0x80, 4096);
> +	drm_intel_bo_unmap(mi_rpc_bo);
> +
> +	emit_report_perf_count(mi_rpc_batch,
> +			       mi_rpc_bo, /* dst */
> +			       0, /* dst offset in bytes */
> +			       0xdeadbeef); /* report ID */
> +
> +	intel_batchbuffer_flush_with_context(mi_rpc_batch, mi_rpc_ctx);
> +
> +	ret = drm_intel_bo_map(mi_rpc_bo, false /* write enable */);
> +	igt_assert_eq(ret, 0);
> +	timestamp = ((uint32_t *)mi_rpc_bo->virtual)[1];
> +	drm_intel_bo_unmap(mi_rpc_bo);
> +
> +	drm_intel_bo_unreference(mi_rpc_bo);
> +	intel_batchbuffer_free(mi_rpc_batch);
> +	drm_intel_gem_context_destroy(mi_rpc_ctx);
> +	drm_intel_bufmgr_destroy(bufmgr);
> +
> +	return timestamp;
> +}
>  
>  static void
>  hsw_sanity_check_render_basic_reports(uint32_t *oa_report0, uint32_t *oa_report1,
> @@ -1032,7 +1188,6 @@ i915_read_reports_until_timestamp(enum drm_i915_oa_format oa_format,
>  	return total_len;
>  }
>  
> -
>  /* CAP_SYS_ADMIN is required to open system wide metrics, unless the system
>   * control parameter dev.i915.perf_stream_paranoid == 0 */
>  static void
> @@ -1347,20 +1502,6 @@ open_and_read_2_oa_reports(int format_id,
>  	__perf_close(stream_fd);
>  }
>  
> -static void
> -gen8_read_report_clock_ratios(uint32_t *report,
> -			      uint32_t *slice_freq_mhz,
> -			      uint32_t *unslice_freq_mhz)
> -{
> -	uint32_t unslice_freq = report[0] & 0x1ff;
> -	uint32_t slice_freq_low = (report[0] >> 25) & 0x7f;
> -	uint32_t slice_freq_high = (report[0] >> 9) & 0x3;
> -	uint32_t slice_freq = slice_freq_low | (slice_freq_high << 7);
> -
> -	*slice_freq_mhz = (slice_freq * 16666) / 1000;
> -	*unslice_freq_mhz = (unslice_freq * 16666) / 1000;
> -}
> -
>  static void
>  print_reports(uint32_t *oa_report0, uint32_t *oa_report1, int fmt)
>  {
> @@ -1552,74 +1693,457 @@ test_oa_formats(void)
>  	}
>  }
>  
> +
> +enum load {
> +	LOW,
> +	HIGH
> +};
> +
> +#define LOAD_HELPER_PAUSE_USEC 500
> +
> +static struct load_helper {
> +	int devid;
> +	int has_ppgtt;
> +	drm_intel_bufmgr *bufmgr;
> +	drm_intel_context *context;
> +	uint32_t context_id;
> +	struct intel_batchbuffer *batch;
> +	drm_intel_bo *target_buffer;
Unused.

> +	enum load load;
> +	bool exit;
> +	struct igt_helper_process igt_proc;
> +	struct igt_buf src, dst;
> +} lh = { 0, };
Isn't this just zero initializing .devid with that stray comma, but then again
this is static so we needn't even bother...

> +
> +static void load_helper_signal_handler(int sig)
> +{
> +	if (sig == SIGUSR2)
> +		lh.load = lh.load == LOW ? HIGH : LOW;
> +	else
> +		lh.exit = true;
> +}
> +
> +static void load_helper_set_load(enum load load)
> +{
> +	igt_assert(lh.igt_proc.running);
> +
> +	if (lh.load == load)
> +		return;
> +
> +	lh.load = load;
> +	kill(lh.igt_proc.pid, SIGUSR2);
> +}
> +
> +static void load_helper_run(enum load load)
> +{
> +	/*
> +	 * FIXME fork helpers won't get cleaned up when started from within a
> +	 * subtest, so handle the case where it sticks around a bit too long.
> +	 */
> +	if (lh.igt_proc.running) {
> +		load_helper_set_load(load);
> +		return;
> +	}
> +
> +	lh.load = load;
> +
> +	igt_fork_helper(&lh.igt_proc) {
> +		signal(SIGUSR1, load_helper_signal_handler);
> +		signal(SIGUSR2, load_helper_signal_handler);
> +
> +		while (!lh.exit) {
> +			int ret;
> +
> +			render_copy(lh.batch,
> +				    lh.context,
> +				    &lh.src, 0, 0, 1920, 1080,
> +				    &lh.dst, 0, 0);
> +
> +			intel_batchbuffer_flush_with_context(lh.batch,
> +							     lh.context);
> +
> +			ret = drm_intel_gem_context_get_id(lh.context,
> +							   &lh.context_id);
> +			igt_assert_eq(ret, 0);
> +
> +			drm_intel_bo_wait_rendering(lh.dst.bo);
> +
> +			/* Lower the load by pausing after every submitted
> +			 * write. */
> +			if (lh.load == LOW)
> +				usleep(LOAD_HELPER_PAUSE_USEC);
> +		}
> +	}
> +}
> +
> +static void load_helper_stop(void)
> +{
> +	kill(lh.igt_proc.pid, SIGUSR1);
> +	igt_assert(igt_wait_helper(&lh.igt_proc) == 0);
> +}
> +
> +static void load_helper_init(void)
> +{
> +	int ret;
> +
> +	lh.devid = intel_get_drm_devid(drm_fd);
> +	lh.has_ppgtt = gem_uses_ppgtt(drm_fd);
> +
> +	/* MI_STORE_DATA can only use GTT address on gen4+/g33 and needs
> +	 * snoopable mem on pre-gen6. Hence load-helper only works on gen6+, but
> +	 * that's also all we care about for the rps testcase*/
> +	igt_assert(intel_gen(lh.devid) >= 6);
> +	lh.bufmgr = drm_intel_bufmgr_gem_init(drm_fd, 4096);
> +	igt_assert(lh.bufmgr);
> +
> +	drm_intel_bufmgr_gem_enable_reuse(lh.bufmgr);
> +
> +	lh.context = drm_intel_gem_context_create(lh.bufmgr);
> +	igt_assert(lh.context);
> +
> +	lh.context_id = 0xffffffff;
> +	ret = drm_intel_gem_context_get_id(lh.context, &lh.context_id);
> +	igt_assert_eq(ret, 0);
> +	igt_assert_neq(lh.context_id, 0xffffffff);
> +
> +	lh.batch = intel_batchbuffer_alloc(lh.bufmgr, lh.devid);
> +	igt_assert(lh.batch);
> +
> +	scratch_buf_init(lh.bufmgr, &lh.dst, 1920, 1080, 0);
> +	scratch_buf_init(lh.bufmgr, &lh.src, 1920, 1080, 0);
> +}
> +
> +static void load_helper_fini(void)
> +{
> +	if (lh.igt_proc.running)
> +		load_helper_stop();
> +
> +	if (lh.src.bo)
> +		drm_intel_bo_unreference(lh.src.bo);
> +	if (lh.dst.bo)
> +		drm_intel_bo_unreference(lh.dst.bo);
> +
> +	if (lh.batch)
> +		intel_batchbuffer_free(lh.batch);
> +
> +	if (lh.context)
> +		drm_intel_gem_context_destroy(lh.context);
> +
> +	if (lh.bufmgr)
> +		drm_intel_bufmgr_destroy(lh.bufmgr);
> +}
> +
>  static void
>  test_oa_exponents(void)
>  {
> -	igt_debug("Testing OA timer exponents\n");
> +	load_helper_init();
> +	load_helper_run(HIGH);
>  
>  	/* It's asking a lot to sample with a 160 nanosecond period and the
>  	 * test can fail due to buffer overflows if it wasn't possible to
>  	 * keep up, so we don't start from an exponent of zero...
>  	 */
> -	for (int i = 5; i < 20; i++) {
> -		uint32_t expected_timestamp_delta;
> -		uint32_t timestamp_delta;
> -		uint32_t oa_report0[64];
> -		uint32_t oa_report1[64];
> +	for (int exponent = 5; exponent < 18; exponent++) {
> +		uint64_t expected_timestamp_delta;
>  		uint32_t time_delta;
> -		uint32_t clock_delta;
> -		uint32_t freq;
>  		int n_tested = 0;
> +		int n_time_delta_matches = 0;
>  
>  		/* The exponent is effectively selecting a bit in the timestamp
>  		 * to trigger reports on and so in practice we expect the raw
>  		 * timestamp deltas for periodic reports to exactly match the
>  		 * value of next bit.
>  		 */
> -		expected_timestamp_delta = 2 << i;
> +		expected_timestamp_delta = 2UL << exponent;
>  
>  		for (int j = 0; n_tested < 10 && j < 100; j++) {
> -			uint32_t ticks0, ticks1;
> -
> -			igt_debug("ITER %d: testing OA exponent %d (period = %"PRIu64"ns)\n",
> -				  j, i, oa_exponent_to_ns(i));
> -
> -			open_and_read_2_oa_reports(test_oa_format,
> -						   i, /* exponent */
> -						   oa_report0,
> -						   oa_report1,
> -						   true); /* timer triggered
> -							     reports only */
> -
> -			timestamp_delta = oa_report1[1] - oa_report0[1];
> -			igt_assert_neq(timestamp_delta, 0);
> -
> -			if (timestamp_delta != expected_timestamp_delta) {
> -				igt_debug("timestamp0 = %u/0x%x\n",
> -					  oa_report0[1], oa_report0[1]);
> -				igt_debug("timestamp1 = %u/0x%x\n",
> -					  oa_report1[1], oa_report1[1]);
> +			uint64_t properties[] = {
> +				/* Include OA reports in samples */
> +				DRM_I915_PERF_PROP_SAMPLE_OA, true,
> +
> +				/* OA unit configuration */
> +				DRM_I915_PERF_PROP_OA_METRICS_SET, test_metric_set_id,
> +				DRM_I915_PERF_PROP_OA_FORMAT, test_oa_format,
> +				DRM_I915_PERF_PROP_OA_EXPONENT, exponent,
> +			};
> +			struct drm_i915_perf_open_param param = {
> +				.flags = I915_PERF_FLAG_FD_CLOEXEC,
> +				.num_properties = ARRAY_SIZE(properties) / 2,
> +				.properties_ptr = to_user_pointer(properties),
> +			};
> +			int ret;
> +			uint64_t average_timestamp_delta;
> +			uint32_t n_reports = 0;
> +			uint32_t n_report_lost = 0;
> +			uint32_t n_idle_reports = 0;
> +			uint32_t n_reads = 0;
> +			uint32_t context_id;
> +			uint64_t first_timestamp = 0;
> +			bool check_first_timestamp = true;
> +			struct drm_i915_perf_record_header *header;
> +			uint64_t delta_delta;
> +			struct {
> +				uint32_t report[64];
> +			} reports[30];
> +			struct {
> +				uint8_t *buf;
> +				size_t len;
> +			} reads[1000];
> +			double error;
> +			double tick_per_period;
> +
> +			igt_debug("ITER %d: testing OA exponent %d,"
> +				  " expected ts delta = %"PRIu64" (%"PRIu64"ns/%.2fus/%.2fms)\n",
> +				  j, exponent,
> +				  expected_timestamp_delta,
> +				  oa_exponent_to_ns(exponent),
> +				  oa_exponent_to_ns(exponent) / 1000.0,
> +				  oa_exponent_to_ns(exponent) / (1000.0 * 1000.0));
> +
> +			stream_fd = __perf_open(drm_fd, &param);
> +
> +			/* Right after opening the OA stream, read a
> +			 * first timestamp as way to filter previously
> +			 * scheduled work that would have configured
> +			 * the OA unit at a different period. */
> +			first_timestamp = i915_get_one_gpu_timestamp(&context_id);
> +
> +			while (n_reads < ARRAY_SIZE(reads) &&
> +			       n_reports < ARRAY_SIZE(reports)) {
> +				const size_t buf_size = 1024 * 1024;
> +				uint8_t *buf = reads[n_reads++].buf = calloc(1, buf_size);
> +
> +				while ((ret = read(stream_fd, buf, buf_size)) < 0 &&
> +				       errno == EINTR)
> +					;
> +
> +				/* We should never have no data. */
> +				igt_assert(ret > 0);
> +				reads[n_reads - 1].len = ret;
> +
> +				igt_debug(" > read %i bytes\n", ret);
> +
> +				for (int offset = 0;
> +				     offset < ret && n_reports < ARRAY_SIZE(reports);
> +				     offset += header->size) {
> +					uint32_t *report;
> +					double previous_tick_per_period;
> +
> +					header = (void *)(buf + offset);
> +
> +					if (header->type == DRM_I915_PERF_RECORD_OA_BUFFER_LOST) {
> +						igt_assert(!"reached");
> +						break;
> +					}
> +
> +					if (header->type == DRM_I915_PERF_RECORD_OA_REPORT_LOST) {
> +						n_report_lost++;
> +						n_reports = 0;
> +						n_report_lost = 0;
Eh?

> +						n_idle_reports = 0;
> +						for (int r = 0; r < n_reads; r++)
> +							free(reads[r].buf);
> +						n_reads = 0;
> +						break;
> +					}
> +
> +					if (header->type != DRM_I915_PERF_RECORD_SAMPLE)
> +						continue;
> +
> +					report = (void *)(header + 1);
> +
> +					/* Skip anything before the first
> +					 * timestamp, it might not be at the
> +					 * right periodic exponent. */
> +					if (check_first_timestamp &&
> +					    report[1] < first_timestamp) {
> +						igt_debug(" > Dropping ts=%u (prior %"PRIu64")\n",
> +							  report[1], first_timestamp);
> +						continue;
> +					}
> +
> +					/* Once we've passed the first
> +					 * timestamp, no need to check. */
> +					check_first_timestamp = false;
> +
> +					if (!oa_report_ctx_is_valid(report))
> +						n_idle_reports++;
> +
> +					/* We only measure timestamps between
> +					 * periodic reports. */
> +					if (!oa_report_is_periodic(exponent, report))
> +						continue;
> +
> +					igt_debug(" > write %i timestamp=%u\n", n_reports, report[1]);
> +					memcpy(reports[n_reports].report, report,
> +					       sizeof(reports[n_reports].report));
> +					n_reports++;
> +
> +					previous_tick_per_period = tick_per_period;
> +
> +					if (n_reports > 1) {
> +						tick_per_period =
> +							oa_reports_tick_per_period(reports[n_reports - 2].report,
> +										   reports[n_reports - 1].report);
> +
> +						/* Dismiss the series of report
> +						 * if we notice clock frequency
> +						 * changes. */
> +						if (!double_value_within(tick_per_period,
> +									 previous_tick_per_period, 5)) {
> +								igt_debug("Noticed clock frequency change at ts=%u (%f / %f), "
> +									  "dropping reports and trying again\n",
> +									  report[1], previous_tick_per_period, tick_per_period);
> +								n_reports = 0;
> +								n_report_lost = 0;
> +								n_idle_reports = 0;
> +								for (int r = 0; r < n_reads; r++)
> +									free(reads[r].buf);
> +								n_reads = 0;
> +								break;
> +						}
> +					}
> +				}
>  			}
>  
> -			igt_assert_eq(timestamp_delta, expected_timestamp_delta);
> +			__perf_close(stream_fd);
> +			igt_debug("closed stream\n");
>  
> -			ticks0 = read_report_ticks(oa_report0, test_oa_format);
> -			ticks1 = read_report_ticks(oa_report1, test_oa_format);
> -			clock_delta = ticks1 - ticks0;
> +			igt_assert_eq(n_reports, ARRAY_SIZE(reports));
>  
> -			time_delta = timebase_scale(timestamp_delta);
> +			average_timestamp_delta = 0;
> +			for (int i = 0; i < (n_reports - 1); i++) {
> +				/* XXX: calculating with u32 arithmetic to account for overflow */
> +				uint32_t u32_delta = reports[i + 1].report[1] - reports[i].report[1];
>  
> -			freq = ((uint64_t)clock_delta * 1000) / time_delta;
> -			igt_debug("ITER %d: time delta = %"PRIu32"(ns) clock delta = %"PRIu32" freq = %"PRIu32"(mhz)\n",
> -				  j, time_delta, clock_delta, freq);
> +				average_timestamp_delta += u32_delta;
> +			}
> +			average_timestamp_delta /= (n_reports - 1);
> +
> +			if (average_timestamp_delta > expected_timestamp_delta)
> +				delta_delta  = average_timestamp_delta - expected_timestamp_delta;
> +			else
> +				delta_delta = expected_timestamp_delta - average_timestamp_delta;
> +			error = (delta_delta / (double)expected_timestamp_delta) * 100.0;
> +
> +			time_delta = timebase_scale(average_timestamp_delta);
> +
> +			igt_debug(" > Avg. time delta = %"PRIu32"(ns),"
> +				  " lost reports = %u, n idle reports = %u,"
> +				  " n reads = %u, error=%f\n",
> +				  time_delta, n_report_lost, n_idle_reports, n_reads, error);
> +			if (error > 5) {
> +				uint32_t *rpt = NULL, *last = NULL, *last_periodic = NULL;
> +
> +				igt_debug(" > More than 5%% error: avg_ts_delta = %"PRIu64", delta_delta = %"PRIu64", "
> +					  "expected_delta = %"PRIu64", first_timestamp = %"PRIu64" ctx_id=%"PRIu32"\n",
> +					  average_timestamp_delta, delta_delta, expected_timestamp_delta, first_timestamp, context_id);
> +				for (int i = 0; i < (n_reports - 1); i++) {
> +					/* XXX: calculating with u32 arithmetic to account for overflow */
> +					uint32_t u32_delta =
> +						reports[i + 1].report[1] - reports[i].report[1];
> +
> +					if (u32_delta > expected_timestamp_delta)
> +						delta_delta  = u32_delta - expected_timestamp_delta;
> +					else
> +						delta_delta = expected_timestamp_delta - u32_delta;
> +					error = (delta_delta / (double)expected_timestamp_delta) * 100.0;
> +
> +					igt_debug(" > ts=%u-%u timestamp delta from %2d to %2d = %-8u (error = %u%%, ctx_id = %x)\n",
> +						  reports[i + 1].report[1], reports[i].report[1],
> +						  i, i + 1, u32_delta, (unsigned)error,
> +						  oa_report_get_ctx_id(reports[i + 1].report));
> +				}
> +				for (int r = 0; r < n_reads; r++) {
> +					igt_debug(" > read\n");
> +					for (int offset = 0;
> +					     offset < reads[r].len;
> +					     offset += header->size) {
> +						int counter_print = 13;
Why counter A13, what's the significance? Perhaps we need a comment...

> +						uint64_t a0 = 0, aN = 0;
> +						double local_period = 0;
> +
> +						header = (void *) &reads[r].buf[offset];
> +
> +						if (header->type != DRM_I915_PERF_RECORD_SAMPLE) {
> +							igt_debug(" > loss\n");
> +							continue;
> +						}
> +
> +						rpt = (void *)(header + 1);
> +
> +						if (last) {
> +							a0 = gen8_read_40bit_a_counter(rpt, test_oa_format, 0) -
> +								gen8_read_40bit_a_counter(last, test_oa_format, 0);
> +							aN = gen8_read_40bit_a_counter(rpt, test_oa_format, counter_print) -
> +								gen8_read_40bit_a_counter(last, test_oa_format, counter_print);
> +						}
> +
> +						if (last_periodic &&
> +						    oa_report_is_periodic(exponent, rpt)) {
> +							local_period =
> +								((uint64_t) rpt[3] - last_periodic[3])  /
> +								((uint64_t) rpt[1] - last_periodic[1]);
Hmm I thought the 'GPU Clock Ticks' was only present on gen8+ reports, since
this is also run on haswell are we not reading a counter here? Do we need to use
the oa_reports_tick_per_period() helper? Some other tests also look suspect, or
am I missing something?

Anyway seems to pass now on my bdw :)

> +						}
> +
> +						igt_debug(" > report ts=%u"
> +							  " ts_delta_last=%8u ts_delta_last_periodic=%8u is_timer=%i ctx_id=%8x gpu_ticks=%u period=%.2f A0=%lu A%i=%lu\n",
> +							  rpt[1],
> +							  (last != NULL) ? (rpt[1] - last[1]) : 0,
> +							  (last_periodic != NULL) ? (rpt[1] - last_periodic[1]) : 0,
> +							  oa_report_is_periodic(exponent, rpt),
> +							  oa_report_get_ctx_id(rpt),
> +							  (last != NULL) ? (rpt[3] - last[3]) : 0,
> +							  local_period,
> +							  a0, counter_print, aN);
> +
> +						last = rpt;
> +						if (oa_report_is_periodic(exponent, rpt))
> +							last_periodic = rpt;
> +					}
> +				}
> +
> +				igt_assert(!"reached");
> +			}
> +
> +			if (timestamp_delta_within(average_timestamp_delta,
> +						   expected_timestamp_delta,
> +						   expected_timestamp_delta * 0.05)) {
> +				igt_debug(" > timestamp delta matching %"PRIu64"ns ~= expected %"PRIu64"! :)\n",
> +					  timebase_scale(average_timestamp_delta),
> +					  timebase_scale(expected_timestamp_delta));
> +				n_time_delta_matches++;
> +			} else {
> +				igt_debug(" > timestamp delta mismatch: %"PRIu64"ns != expected %"PRIu64"ns\n",
> +					  timebase_scale(average_timestamp_delta),
> +					  timebase_scale(expected_timestamp_delta));
> +				igt_assert(average_timestamp_delta <
> +					   (expected_timestamp_delta * 2));
> +			}
>  
>  			n_tested++;
> +
> +			for (int r = 0; r < n_reads; r++)
> +				free(reads[r].buf);
>  		}
>  
>  		if (n_tested < 10)
> -			igt_debug("sysfs frequency pinning too unstable for cross-referencing with OA derived frequency");
> +			igt_debug("Too many test iterations had to be skipped\n");
>  		igt_assert_eq(n_tested, 10);
> +
> +		igt_debug("Number of iterations with expected timestamp delta = %d\n",
> +			  n_time_delta_matches);
> +
> +		/* The HW doesn't give us any strict guarantee that the
> +		 * timestamps are exactly aligned with the exponent mask but
> +		 * in practice it seems very rare for that not to be the case
> +		 * so it a useful sanity check to assert quite strictly...
> +		 */
> +		igt_assert(n_time_delta_matches >= 9);
>  	}
> +
> +	load_helper_stop();
> +	load_helper_fini();
>  }
>  
>  /* The OA exponent selects a timestamp counter bit to trigger reports on.
> @@ -2485,32 +3009,6 @@ test_disabled_read_error(void)
>  	__perf_close(stream_fd);
>  }
>  
> -static void
> -emit_report_perf_count(struct intel_batchbuffer *batch,
> -		       drm_intel_bo *dst_bo,
> -		       int dst_offset,
> -		       uint32_t report_id)
> -{
> -	if (IS_HASWELL(devid)) {
> -		BEGIN_BATCH(3, 1);
> -		OUT_BATCH(GEN6_MI_REPORT_PERF_COUNT);
> -		OUT_RELOC(dst_bo, I915_GEM_DOMAIN_INSTRUCTION, I915_GEM_DOMAIN_INSTRUCTION,
> -			  dst_offset);
> -		OUT_BATCH(report_id);
> -		ADVANCE_BATCH();
> -	} else {
> -		/* XXX: NB: n dwords arg is actually magic since it internally
> -		 * automatically accounts for larger addresses on gen >= 8...
> -		 */
> -		BEGIN_BATCH(3, 1);
> -		OUT_BATCH(GEN8_MI_REPORT_PERF_COUNT);
> -		OUT_RELOC(dst_bo, I915_GEM_DOMAIN_INSTRUCTION, I915_GEM_DOMAIN_INSTRUCTION,
> -			  dst_offset);
> -		OUT_BATCH(report_id);
> -		ADVANCE_BATCH();
> -	}
> -}
> -
>  static void
>  test_mi_rpc(void)
>  {
> @@ -2580,38 +3078,6 @@ test_mi_rpc(void)
>  	__perf_close(stream_fd);
>  }
>  
> -static void
> -scratch_buf_memset(drm_intel_bo *bo, int width, int height, uint32_t color)
> -{
> -	int ret;
> -
> -	ret = drm_intel_bo_map(bo, true /* writable */);
> -	igt_assert_eq(ret, 0);
> -
> -	for (int i = 0; i < width * height; i++)
> -		((uint32_t *)bo->virtual)[i] = color;
> -
> -	drm_intel_bo_unmap(bo);
> -}
> -
> -static void
> -scratch_buf_init(drm_intel_bufmgr *bufmgr,
> -		 struct igt_buf *buf,
> -		 int width, int height,
> -		 uint32_t color)
> -{
> -	size_t stride = width * 4;
> -	size_t size = stride * height;
> -	drm_intel_bo *bo = drm_intel_bo_alloc(bufmgr, "", size, 4096);
> -
> -	scratch_buf_memset(bo, width, height, color);
> -
> -	buf->bo = bo;
> -	buf->stride = stride;
> -	buf->tiling = I915_TILING_NONE;
> -	buf->size = size;
> -}
> -
>  static void
>  emit_stall_timestamp_and_rpc(struct intel_batchbuffer *batch,
>  			     drm_intel_bo *dst,
> -- 
> 2.14.1
> 
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