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drm/i915/selftests: Measure dispatch latency
authorChris Wilson <chris@chris-wilson.co.uk>
Tue, 19 May 2020 13:08:02 +0000 (14:08 +0100)
committerChris Wilson <chris@chris-wilson.co.uk>
Tue, 19 May 2020 14:28:26 +0000 (15:28 +0100)
A useful metric of the system's health is how fast we can tell the GPU
to do various actions, so measure our latency.

v2: Refactor all the instruction building into emitters.
v3: Mark the error handling if not perfect, at least consistent.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200519130802.4067-1-chris@chris-wilson.co.uk
drivers/gpu/drm/i915/selftests/i915_request.c

index 6014e8d..92c628f 100644 (file)
 
 #include <linux/prime_numbers.h>
 #include <linux/pm_qos.h>
+#include <linux/sort.h>
 
 #include "gem/i915_gem_pm.h"
 #include "gem/selftests/mock_context.h"
 
+#include "gt/intel_engine_heartbeat.h"
 #include "gt/intel_engine_pm.h"
 #include "gt/intel_engine_user.h"
 #include "gt/intel_gt.h"
+#include "gt/intel_gt_requests.h"
 
 #include "i915_random.h"
 #include "i915_selftest.h"
+#include "igt_flush_test.h"
 #include "igt_live_test.h"
 #include "igt_spinner.h"
 #include "lib_sw_fence.h"
@@ -1524,6 +1528,824 @@ struct perf_series {
        struct intel_context *ce[];
 };
 
+static int cmp_u32(const void *A, const void *B)
+{
+       const u32 *a = A, *b = B;
+
+       return *a - *b;
+}
+
+static u32 trifilter(u32 *a)
+{
+       u64 sum;
+
+#define TF_COUNT 5
+       sort(a, TF_COUNT, sizeof(*a), cmp_u32, NULL);
+
+       sum = mul_u32_u32(a[2], 2);
+       sum += a[1];
+       sum += a[3];
+
+       GEM_BUG_ON(sum > U32_MAX);
+       return sum;
+#define TF_BIAS 2
+}
+
+static u64 cycles_to_ns(struct intel_engine_cs *engine, u32 cycles)
+{
+       u64 ns = i915_cs_timestamp_ticks_to_ns(engine->i915, cycles);
+
+       return DIV_ROUND_CLOSEST(ns, 1 << TF_BIAS);
+}
+
+static u32 *emit_timestamp_store(u32 *cs, struct intel_context *ce, u32 offset)
+{
+       *cs++ = MI_STORE_REGISTER_MEM_GEN8 | MI_USE_GGTT;
+       *cs++ = i915_mmio_reg_offset(RING_TIMESTAMP((ce->engine->mmio_base)));
+       *cs++ = offset;
+       *cs++ = 0;
+
+       return cs;
+}
+
+static u32 *emit_store_dw(u32 *cs, u32 offset, u32 value)
+{
+       *cs++ = MI_STORE_DWORD_IMM_GEN4 | MI_USE_GGTT;
+       *cs++ = offset;
+       *cs++ = 0;
+       *cs++ = value;
+
+       return cs;
+}
+
+static u32 *emit_semaphore_poll(u32 *cs, u32 mode, u32 value, u32 offset)
+{
+       *cs++ = MI_SEMAPHORE_WAIT |
+               MI_SEMAPHORE_GLOBAL_GTT |
+               MI_SEMAPHORE_POLL |
+               mode;
+       *cs++ = value;
+       *cs++ = offset;
+       *cs++ = 0;
+
+       return cs;
+}
+
+static u32 *emit_semaphore_poll_until(u32 *cs, u32 offset, u32 value)
+{
+       return emit_semaphore_poll(cs, MI_SEMAPHORE_SAD_EQ_SDD, value, offset);
+}
+
+static void semaphore_set(u32 *sema, u32 value)
+{
+       WRITE_ONCE(*sema, value);
+       wmb(); /* flush the update to the cache, and beyond */
+}
+
+static u32 *hwsp_scratch(const struct intel_context *ce)
+{
+       return memset32(ce->engine->status_page.addr + 1000, 0, 21);
+}
+
+static u32 hwsp_offset(const struct intel_context *ce, u32 *dw)
+{
+       return (i915_ggtt_offset(ce->engine->status_page.vma) +
+               offset_in_page(dw));
+}
+
+static int measure_semaphore_response(struct intel_context *ce)
+{
+       u32 *sema = hwsp_scratch(ce);
+       const u32 offset = hwsp_offset(ce, sema);
+       u32 elapsed[TF_COUNT], cycles;
+       struct i915_request *rq;
+       u32 *cs;
+       int err;
+       int i;
+
+       /*
+        * Measure how many cycles it takes for the HW to detect the change
+        * in a semaphore value.
+        *
+        *    A: read CS_TIMESTAMP from CPU
+        *    poke semaphore
+        *    B: read CS_TIMESTAMP on GPU
+        *
+        * Semaphore latency: B - A
+        */
+
+       semaphore_set(sema, -1);
+
+       rq = i915_request_create(ce);
+       if (IS_ERR(rq))
+               return PTR_ERR(rq);
+
+       cs = intel_ring_begin(rq, 4 + 12 * ARRAY_SIZE(elapsed));
+       if (IS_ERR(cs)) {
+               i915_request_add(rq);
+               err = PTR_ERR(cs);
+               goto err;
+       }
+
+       cs = emit_store_dw(cs, offset, 0);
+       for (i = 1; i <= ARRAY_SIZE(elapsed); i++) {
+               cs = emit_semaphore_poll_until(cs, offset, i);
+               cs = emit_timestamp_store(cs, ce, offset + i * sizeof(u32));
+               cs = emit_store_dw(cs, offset, 0);
+       }
+
+       intel_ring_advance(rq, cs);
+       i915_request_add(rq);
+
+       if (wait_for(READ_ONCE(*sema) == 0, 50)) {
+               err = -EIO;
+               goto err;
+       }
+
+       for (i = 1; i <= ARRAY_SIZE(elapsed); i++) {
+               preempt_disable();
+               cycles = ENGINE_READ_FW(ce->engine, RING_TIMESTAMP);
+               semaphore_set(sema, i);
+               preempt_enable();
+
+               if (wait_for(READ_ONCE(*sema) == 0, 50)) {
+                       err = -EIO;
+                       goto err;
+               }
+
+               elapsed[i - 1] = sema[i] - cycles;
+       }
+
+       cycles = trifilter(elapsed);
+       pr_info("%s: semaphore response %d cycles, %lluns\n",
+               ce->engine->name, cycles >> TF_BIAS,
+               cycles_to_ns(ce->engine, cycles));
+
+       return intel_gt_wait_for_idle(ce->engine->gt, HZ);
+
+err:
+       intel_gt_set_wedged(ce->engine->gt);
+       return err;
+}
+
+static int measure_idle_dispatch(struct intel_context *ce)
+{
+       u32 *sema = hwsp_scratch(ce);
+       const u32 offset = hwsp_offset(ce, sema);
+       u32 elapsed[TF_COUNT], cycles;
+       u32 *cs;
+       int err;
+       int i;
+
+       /*
+        * Measure how long it takes for us to submit a request while the
+        * engine is idle, but is resting in our context.
+        *
+        *    A: read CS_TIMESTAMP from CPU
+        *    submit request
+        *    B: read CS_TIMESTAMP on GPU
+        *
+        * Submission latency: B - A
+        */
+
+       for (i = 0; i < ARRAY_SIZE(elapsed); i++) {
+               struct i915_request *rq;
+
+               err = intel_gt_wait_for_idle(ce->engine->gt, HZ / 2);
+               if (err)
+                       return err;
+
+               rq = i915_request_create(ce);
+               if (IS_ERR(rq)) {
+                       err = PTR_ERR(rq);
+                       goto err;
+               }
+
+               cs = intel_ring_begin(rq, 4);
+               if (IS_ERR(cs)) {
+                       i915_request_add(rq);
+                       err = PTR_ERR(cs);
+                       goto err;
+               }
+
+               cs = emit_timestamp_store(cs, ce, offset + i * sizeof(u32));
+
+               intel_ring_advance(rq, cs);
+
+               preempt_disable();
+               local_bh_disable();
+               elapsed[i] = ENGINE_READ_FW(ce->engine, RING_TIMESTAMP);
+               i915_request_add(rq);
+               local_bh_enable();
+               preempt_enable();
+       }
+
+       err = intel_gt_wait_for_idle(ce->engine->gt, HZ / 2);
+       if (err)
+               goto err;
+
+       for (i = 0; i < ARRAY_SIZE(elapsed); i++)
+               elapsed[i] = sema[i] - elapsed[i];
+
+       cycles = trifilter(elapsed);
+       pr_info("%s: idle dispatch latency %d cycles, %lluns\n",
+               ce->engine->name, cycles >> TF_BIAS,
+               cycles_to_ns(ce->engine, cycles));
+
+       return intel_gt_wait_for_idle(ce->engine->gt, HZ);
+
+err:
+       intel_gt_set_wedged(ce->engine->gt);
+       return err;
+}
+
+static int measure_busy_dispatch(struct intel_context *ce)
+{
+       u32 *sema = hwsp_scratch(ce);
+       const u32 offset = hwsp_offset(ce, sema);
+       u32 elapsed[TF_COUNT + 1], cycles;
+       u32 *cs;
+       int err;
+       int i;
+
+       /*
+        * Measure how long it takes for us to submit a request while the
+        * engine is busy, polling on a semaphore in our context. With
+        * direct submission, this will include the cost of a lite restore.
+        *
+        *    A: read CS_TIMESTAMP from CPU
+        *    submit request
+        *    B: read CS_TIMESTAMP on GPU
+        *
+        * Submission latency: B - A
+        */
+
+       for (i = 1; i <= ARRAY_SIZE(elapsed); i++) {
+               struct i915_request *rq;
+
+               rq = i915_request_create(ce);
+               if (IS_ERR(rq)) {
+                       err = PTR_ERR(rq);
+                       goto err;
+               }
+
+               cs = intel_ring_begin(rq, 12);
+               if (IS_ERR(cs)) {
+                       i915_request_add(rq);
+                       err = PTR_ERR(cs);
+                       goto err;
+               }
+
+               cs = emit_store_dw(cs, offset + i * sizeof(u32), -1);
+               cs = emit_semaphore_poll_until(cs, offset, i);
+               cs = emit_timestamp_store(cs, ce, offset + i * sizeof(u32));
+
+               intel_ring_advance(rq, cs);
+
+               if (i > 1 && wait_for(READ_ONCE(sema[i - 1]), 500)) {
+                       err = -EIO;
+                       goto err;
+               }
+
+               preempt_disable();
+               local_bh_disable();
+               elapsed[i - 1] = ENGINE_READ_FW(ce->engine, RING_TIMESTAMP);
+               i915_request_add(rq);
+               local_bh_enable();
+               semaphore_set(sema, i - 1);
+               preempt_enable();
+       }
+
+       wait_for(READ_ONCE(sema[i - 1]), 500);
+       semaphore_set(sema, i - 1);
+
+       for (i = 1; i <= TF_COUNT; i++) {
+               GEM_BUG_ON(sema[i] == -1);
+               elapsed[i - 1] = sema[i] - elapsed[i];
+       }
+
+       cycles = trifilter(elapsed);
+       pr_info("%s: busy dispatch latency %d cycles, %lluns\n",
+               ce->engine->name, cycles >> TF_BIAS,
+               cycles_to_ns(ce->engine, cycles));
+
+       return intel_gt_wait_for_idle(ce->engine->gt, HZ);
+
+err:
+       intel_gt_set_wedged(ce->engine->gt);
+       return err;
+}
+
+static int plug(struct intel_engine_cs *engine, u32 *sema, u32 mode, int value)
+{
+       const u32 offset =
+               i915_ggtt_offset(engine->status_page.vma) +
+               offset_in_page(sema);
+       struct i915_request *rq;
+       u32 *cs;
+
+       rq = i915_request_create(engine->kernel_context);
+       if (IS_ERR(rq))
+               return PTR_ERR(rq);
+
+       cs = intel_ring_begin(rq, 4);
+       if (IS_ERR(cs)) {
+               i915_request_add(rq);
+               return PTR_ERR(cs);
+       }
+
+       cs = emit_semaphore_poll(cs, mode, value, offset);
+
+       intel_ring_advance(rq, cs);
+       i915_request_add(rq);
+
+       return 0;
+}
+
+static int measure_inter_request(struct intel_context *ce)
+{
+       u32 *sema = hwsp_scratch(ce);
+       const u32 offset = hwsp_offset(ce, sema);
+       u32 elapsed[TF_COUNT + 1], cycles;
+       struct i915_sw_fence *submit;
+       int i, err;
+
+       /*
+        * Measure how long it takes to advance from one request into the
+        * next. Between each request we flush the GPU caches to memory,
+        * update the breadcrumbs, and then invalidate those caches.
+        * We queue up all the requests to be submitted in one batch so
+        * it should be one set of contiguous measurements.
+        *
+        *    A: read CS_TIMESTAMP on GPU
+        *    advance request
+        *    B: read CS_TIMESTAMP on GPU
+        *
+        * Request latency: B - A
+        */
+
+       err = plug(ce->engine, sema, MI_SEMAPHORE_SAD_NEQ_SDD, 0);
+       if (err)
+               return err;
+
+       submit = heap_fence_create(GFP_KERNEL);
+       if (!submit) {
+               semaphore_set(sema, 1);
+               return -ENOMEM;
+       }
+
+       intel_engine_flush_submission(ce->engine);
+       for (i = 1; i <= ARRAY_SIZE(elapsed); i++) {
+               struct i915_request *rq;
+               u32 *cs;
+
+               rq = i915_request_create(ce);
+               if (IS_ERR(rq)) {
+                       err = PTR_ERR(rq);
+                       goto err_submit;
+               }
+
+               err = i915_sw_fence_await_sw_fence_gfp(&rq->submit,
+                                                      submit,
+                                                      GFP_KERNEL);
+               if (err < 0) {
+                       i915_request_add(rq);
+                       goto err_submit;
+               }
+
+               cs = intel_ring_begin(rq, 4);
+               if (IS_ERR(cs)) {
+                       i915_request_add(rq);
+                       err = PTR_ERR(cs);
+                       goto err_submit;
+               }
+
+               cs = emit_timestamp_store(cs, ce, offset + i * sizeof(u32));
+
+               intel_ring_advance(rq, cs);
+               i915_request_add(rq);
+       }
+       local_bh_disable();
+       i915_sw_fence_commit(submit);
+       local_bh_enable();
+       intel_engine_flush_submission(ce->engine);
+       heap_fence_put(submit);
+
+       semaphore_set(sema, 1);
+       err = intel_gt_wait_for_idle(ce->engine->gt, HZ / 2);
+       if (err)
+               goto err;
+
+       for (i = 1; i <= TF_COUNT; i++)
+               elapsed[i - 1] = sema[i + 1] - sema[i];
+
+       cycles = trifilter(elapsed);
+       pr_info("%s: inter-request latency %d cycles, %lluns\n",
+               ce->engine->name, cycles >> TF_BIAS,
+               cycles_to_ns(ce->engine, cycles));
+
+       return intel_gt_wait_for_idle(ce->engine->gt, HZ);
+
+err_submit:
+       i915_sw_fence_commit(submit);
+       heap_fence_put(submit);
+       semaphore_set(sema, 1);
+err:
+       intel_gt_set_wedged(ce->engine->gt);
+       return err;
+}
+
+static int measure_context_switch(struct intel_context *ce)
+{
+       u32 *sema = hwsp_scratch(ce);
+       const u32 offset = hwsp_offset(ce, sema);
+       struct i915_request *fence = NULL;
+       u32 elapsed[TF_COUNT + 1], cycles;
+       int i, j, err;
+       u32 *cs;
+
+       /*
+        * Measure how long it takes to advance from one request in one
+        * context to a request in another context. This allows us to
+        * measure how long the context save/restore take, along with all
+        * the inter-context setup we require.
+        *
+        *    A: read CS_TIMESTAMP on GPU
+        *    switch context
+        *    B: read CS_TIMESTAMP on GPU
+        *
+        * Context switch latency: B - A
+        */
+
+       err = plug(ce->engine, sema, MI_SEMAPHORE_SAD_NEQ_SDD, 0);
+       if (err)
+               return err;
+
+       for (i = 1; i <= ARRAY_SIZE(elapsed); i++) {
+               struct intel_context *arr[] = {
+                       ce, ce->engine->kernel_context
+               };
+               u32 addr = offset + ARRAY_SIZE(arr) * i * sizeof(u32);
+
+               for (j = 0; j < ARRAY_SIZE(arr); j++) {
+                       struct i915_request *rq;
+
+                       rq = i915_request_create(arr[j]);
+                       if (IS_ERR(rq)) {
+                               err = PTR_ERR(rq);
+                               goto err_fence;
+                       }
+
+                       if (fence) {
+                               err = i915_request_await_dma_fence(rq,
+                                                                  &fence->fence);
+                               if (err) {
+                                       i915_request_add(rq);
+                                       goto err_fence;
+                               }
+                       }
+
+                       cs = intel_ring_begin(rq, 4);
+                       if (IS_ERR(cs)) {
+                               i915_request_add(rq);
+                               err = PTR_ERR(cs);
+                               goto err_fence;
+                       }
+
+                       cs = emit_timestamp_store(cs, ce, addr);
+                       addr += sizeof(u32);
+
+                       intel_ring_advance(rq, cs);
+
+                       i915_request_put(fence);
+                       fence = i915_request_get(rq);
+
+                       i915_request_add(rq);
+               }
+       }
+       i915_request_put(fence);
+       intel_engine_flush_submission(ce->engine);
+
+       semaphore_set(sema, 1);
+       err = intel_gt_wait_for_idle(ce->engine->gt, HZ / 2);
+       if (err)
+               goto err;
+
+       for (i = 1; i <= TF_COUNT; i++)
+               elapsed[i - 1] = sema[2 * i + 2] - sema[2 * i + 1];
+
+       cycles = trifilter(elapsed);
+       pr_info("%s: context switch latency %d cycles, %lluns\n",
+               ce->engine->name, cycles >> TF_BIAS,
+               cycles_to_ns(ce->engine, cycles));
+
+       return intel_gt_wait_for_idle(ce->engine->gt, HZ);
+
+err_fence:
+       i915_request_put(fence);
+       semaphore_set(sema, 1);
+err:
+       intel_gt_set_wedged(ce->engine->gt);
+       return err;
+}
+
+static int measure_preemption(struct intel_context *ce)
+{
+       u32 *sema = hwsp_scratch(ce);
+       const u32 offset = hwsp_offset(ce, sema);
+       u32 elapsed[TF_COUNT], cycles;
+       u32 *cs;
+       int err;
+       int i;
+
+       /*
+        * We measure two latencies while triggering preemption. The first
+        * latency is how long it takes for us to submit a preempting request.
+        * The second latency is how it takes for us to return from the
+        * preemption back to the original context.
+        *
+        *    A: read CS_TIMESTAMP from CPU
+        *    submit preemption
+        *    B: read CS_TIMESTAMP on GPU (in preempting context)
+        *    context switch
+        *    C: read CS_TIMESTAMP on GPU (in original context)
+        *
+        * Preemption dispatch latency: B - A
+        * Preemption switch latency: C - B
+        */
+
+       if (!intel_engine_has_preemption(ce->engine))
+               return 0;
+
+       for (i = 1; i <= ARRAY_SIZE(elapsed); i++) {
+               u32 addr = offset + 2 * i * sizeof(u32);
+               struct i915_request *rq;
+
+               rq = i915_request_create(ce);
+               if (IS_ERR(rq)) {
+                       err = PTR_ERR(rq);
+                       goto err;
+               }
+
+               cs = intel_ring_begin(rq, 12);
+               if (IS_ERR(cs)) {
+                       i915_request_add(rq);
+                       err = PTR_ERR(cs);
+                       goto err;
+               }
+
+               cs = emit_store_dw(cs, addr, -1);
+               cs = emit_semaphore_poll_until(cs, offset, i);
+               cs = emit_timestamp_store(cs, ce, addr + sizeof(u32));
+
+               intel_ring_advance(rq, cs);
+               i915_request_add(rq);
+
+               if (wait_for(READ_ONCE(sema[2 * i]) == -1, 500)) {
+                       err = -EIO;
+                       goto err;
+               }
+
+               rq = i915_request_create(ce->engine->kernel_context);
+               if (IS_ERR(rq)) {
+                       err = PTR_ERR(rq);
+                       goto err;
+               }
+
+               cs = intel_ring_begin(rq, 8);
+               if (IS_ERR(cs)) {
+                       i915_request_add(rq);
+                       err = PTR_ERR(cs);
+                       goto err;
+               }
+
+               cs = emit_timestamp_store(cs, ce, addr);
+               cs = emit_store_dw(cs, offset, i);
+
+               intel_ring_advance(rq, cs);
+               rq->sched.attr.priority = I915_PRIORITY_BARRIER;
+
+               elapsed[i - 1] = ENGINE_READ_FW(ce->engine, RING_TIMESTAMP);
+               i915_request_add(rq);
+       }
+
+       if (wait_for(READ_ONCE(sema[2 * i - 2]) != -1, 500)) {
+               err = -EIO;
+               goto err;
+       }
+
+       for (i = 1; i <= TF_COUNT; i++)
+               elapsed[i - 1] = sema[2 * i + 0] - elapsed[i - 1];
+
+       cycles = trifilter(elapsed);
+       pr_info("%s: preemption dispatch latency %d cycles, %lluns\n",
+               ce->engine->name, cycles >> TF_BIAS,
+               cycles_to_ns(ce->engine, cycles));
+
+       for (i = 1; i <= TF_COUNT; i++)
+               elapsed[i - 1] = sema[2 * i + 1] - sema[2 * i + 0];
+
+       cycles = trifilter(elapsed);
+       pr_info("%s: preemption switch latency %d cycles, %lluns\n",
+               ce->engine->name, cycles >> TF_BIAS,
+               cycles_to_ns(ce->engine, cycles));
+
+       return intel_gt_wait_for_idle(ce->engine->gt, HZ);
+
+err:
+       intel_gt_set_wedged(ce->engine->gt);
+       return err;
+}
+
+struct signal_cb {
+       struct dma_fence_cb base;
+       bool seen;
+};
+
+static void signal_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
+{
+       struct signal_cb *s = container_of(cb, typeof(*s), base);
+
+       smp_store_mb(s->seen, true); /* be safe, be strong */
+}
+
+static int measure_completion(struct intel_context *ce)
+{
+       u32 *sema = hwsp_scratch(ce);
+       const u32 offset = hwsp_offset(ce, sema);
+       u32 elapsed[TF_COUNT], cycles;
+       u32 *cs;
+       int err;
+       int i;
+
+       /*
+        * Measure how long it takes for the signal (interrupt) to be
+        * sent from the GPU to be processed by the CPU.
+        *
+        *    A: read CS_TIMESTAMP on GPU
+        *    signal
+        *    B: read CS_TIMESTAMP from CPU
+        *
+        * Completion latency: B - A
+        */
+
+       for (i = 1; i <= ARRAY_SIZE(elapsed); i++) {
+               struct signal_cb cb = { .seen = false };
+               struct i915_request *rq;
+
+               rq = i915_request_create(ce);
+               if (IS_ERR(rq)) {
+                       err = PTR_ERR(rq);
+                       goto err;
+               }
+
+               cs = intel_ring_begin(rq, 12);
+               if (IS_ERR(cs)) {
+                       i915_request_add(rq);
+                       err = PTR_ERR(cs);
+                       goto err;
+               }
+
+               cs = emit_store_dw(cs, offset + i * sizeof(u32), -1);
+               cs = emit_semaphore_poll_until(cs, offset, i);
+               cs = emit_timestamp_store(cs, ce, offset + i * sizeof(u32));
+
+               intel_ring_advance(rq, cs);
+
+               dma_fence_add_callback(&rq->fence, &cb.base, signal_cb);
+
+               local_bh_disable();
+               i915_request_add(rq);
+               local_bh_enable();
+
+               if (wait_for(READ_ONCE(sema[i]) == -1, 50)) {
+                       err = -EIO;
+                       goto err;
+               }
+
+               preempt_disable();
+               semaphore_set(sema, i);
+               while (!READ_ONCE(cb.seen))
+                       cpu_relax();
+
+               elapsed[i - 1] = ENGINE_READ_FW(ce->engine, RING_TIMESTAMP);
+               preempt_enable();
+       }
+
+       err = intel_gt_wait_for_idle(ce->engine->gt, HZ / 2);
+       if (err)
+               goto err;
+
+       for (i = 0; i < ARRAY_SIZE(elapsed); i++) {
+               GEM_BUG_ON(sema[i + 1] == -1);
+               elapsed[i] = elapsed[i] - sema[i + 1];
+       }
+
+       cycles = trifilter(elapsed);
+       pr_info("%s: completion latency %d cycles, %lluns\n",
+               ce->engine->name, cycles >> TF_BIAS,
+               cycles_to_ns(ce->engine, cycles));
+
+       return intel_gt_wait_for_idle(ce->engine->gt, HZ);
+
+err:
+       intel_gt_set_wedged(ce->engine->gt);
+       return err;
+}
+
+static void rps_pin(struct intel_gt *gt)
+{
+       /* Pin the frequency to max */
+       atomic_inc(&gt->rps.num_waiters);
+       intel_uncore_forcewake_get(gt->uncore, FORCEWAKE_ALL);
+
+       mutex_lock(&gt->rps.lock);
+       intel_rps_set(&gt->rps, gt->rps.max_freq);
+       mutex_unlock(&gt->rps.lock);
+}
+
+static void rps_unpin(struct intel_gt *gt)
+{
+       intel_uncore_forcewake_put(gt->uncore, FORCEWAKE_ALL);
+       atomic_dec(&gt->rps.num_waiters);
+}
+
+static void engine_heartbeat_disable(struct intel_engine_cs *engine)
+{
+       engine->props.heartbeat_interval_ms = 0;
+
+       intel_engine_pm_get(engine);
+       intel_engine_park_heartbeat(engine);
+}
+
+static void engine_heartbeat_enable(struct intel_engine_cs *engine)
+{
+       intel_engine_pm_put(engine);
+
+       engine->props.heartbeat_interval_ms =
+               engine->defaults.heartbeat_interval_ms;
+}
+
+static int perf_request_latency(void *arg)
+{
+       struct drm_i915_private *i915 = arg;
+       struct intel_engine_cs *engine;
+       struct pm_qos_request qos;
+       int err = 0;
+
+       if (INTEL_GEN(i915) < 8) /* per-engine CS timestamp, semaphores */
+               return 0;
+
+       cpu_latency_qos_add_request(&qos, 0); /* disable cstates */
+
+       for_each_uabi_engine(engine, i915) {
+               struct intel_context *ce;
+
+               ce = intel_context_create(engine);
+               if (IS_ERR(ce))
+                       goto out;
+
+               err = intel_context_pin(ce);
+               if (err) {
+                       intel_context_put(ce);
+                       goto out;
+               }
+
+               engine_heartbeat_disable(engine);
+               rps_pin(engine->gt);
+
+               if (err == 0)
+                       err = measure_semaphore_response(ce);
+               if (err == 0)
+                       err = measure_idle_dispatch(ce);
+               if (err == 0)
+                       err = measure_busy_dispatch(ce);
+               if (err == 0)
+                       err = measure_inter_request(ce);
+               if (err == 0)
+                       err = measure_context_switch(ce);
+               if (err == 0)
+                       err = measure_preemption(ce);
+               if (err == 0)
+                       err = measure_completion(ce);
+
+               rps_unpin(engine->gt);
+               engine_heartbeat_enable(engine);
+
+               intel_context_unpin(ce);
+               intel_context_put(ce);
+               if (err)
+                       goto out;
+       }
+
+out:
+       if (igt_flush_test(i915))
+               err = -EIO;
+
+       cpu_latency_qos_remove_request(&qos);
+       return err;
+}
+
 static int s_sync0(void *arg)
 {
        struct perf_series *ps = arg;
@@ -2042,6 +2864,7 @@ static int perf_parallel_engines(void *arg)
 int i915_request_perf_selftests(struct drm_i915_private *i915)
 {
        static const struct i915_subtest tests[] = {
+               SUBTEST(perf_request_latency),
                SUBTEST(perf_series_engines),
                SUBTEST(perf_parallel_engines),
        };