drm/i915/selftests: Basic stress test for rapid context switching

We need to exercise the HW and submission paths for switching contexts
rapidly to check that features such as execlists' wa_tail are adequate.
Plus it's an interesting baseline latency metric.

v2: Check the initial request for allocation errors
v3: Use finite waits for more robust handling of broken code

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180920105809.1872-1-chris@chris-wilson.co.uk

1 files changed, 195 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/selftests/i915_gem_context.c b/drivers/gpu/drm/i915/selftests/i915_gem_context.c
index 07d700b7cb94..441a51d4aa54 100644
--- a/drivers/gpu/drm/i915/selftests/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/selftests/i915_gem_context.c
@@ -22,6 +22,8 @@
  *
  */
 
+#include <linux/prime_numbers.h>
+
 #include "../i915_selftest.h"
 #include "i915_random.h"
 #include "igt_flush_test.h"
@@ -32,6 +34,198 @@
 
 #define DW_PER_PAGE (PAGE_SIZE / sizeof(u32))
 
+struct live_test {
+        struct drm_i915_private *i915;
+        const char *func;
+        const char *name;
+
+        unsigned int reset_count;
+};
+
+static int begin_live_test(struct live_test *t,
+                           struct drm_i915_private *i915,
+                           const char *func,
+                           const char *name)
+{
+        int err;
+
+        t->i915 = i915;
+        t->func = func;
+        t->name = name;
+
+        err = i915_gem_wait_for_idle(i915,
+                                     I915_WAIT_LOCKED,
+                                     MAX_SCHEDULE_TIMEOUT);
+        if (err) {
+                pr_err("%s(%s): failed to idle before, with err=%d!",
+                       func, name, err);
+                return err;
+        }
+
+        i915->gpu_error.missed_irq_rings = 0;
+        t->reset_count = i915_reset_count(&i915->gpu_error);
+
+        return 0;
+}
+
+static int end_live_test(struct live_test *t)
+{
+        struct drm_i915_private *i915 = t->i915;
+
+        if (igt_flush_test(i915, I915_WAIT_LOCKED))
+                return -EIO;
+
+        if (t->reset_count != i915_reset_count(&i915->gpu_error)) {
+                pr_err("%s(%s): GPU was reset %d times!\n",
+                       t->func, t->name,
+                       i915_reset_count(&i915->gpu_error) - t->reset_count);
+                return -EIO;
+        }
+
+        if (i915->gpu_error.missed_irq_rings) {
+                pr_err("%s(%s): Missed interrupts on engines %lx\n",
+                       t->func, t->name, i915->gpu_error.missed_irq_rings);
+                return -EIO;
+        }
+
+        return 0;
+}
+
+static int live_nop_switch(void *arg)
+{
+        const unsigned int nctx = 1024;
+        struct drm_i915_private *i915 = arg;
+        struct intel_engine_cs *engine;
+        struct i915_gem_context **ctx;
+        enum intel_engine_id id;
+        struct drm_file *file;
+        struct live_test t;
+        unsigned long n;
+        int err = -ENODEV;
+
+        /*
+         * Create as many contexts as we can feasibly get away with
+         * and check we can switch between them rapidly.
+         *
+         * Serves as very simple stress test for submission and HW switching
+         * between contexts.
+         */
+
+        if (!DRIVER_CAPS(i915)->has_logical_contexts)
+                return 0;
+
+        file = mock_file(i915);
+        if (IS_ERR(file))
+                return PTR_ERR(file);
+
+        mutex_lock(&i915->drm.struct_mutex);
+
+        ctx = kcalloc(nctx, sizeof(*ctx), GFP_KERNEL);
+        if (!ctx) {
+                err = -ENOMEM;
+                goto out_unlock;
+        }
+
+        for (n = 0; n < nctx; n++) {
+                ctx[n] = i915_gem_create_context(i915, file->driver_priv);
+                if (IS_ERR(ctx[n])) {
+                        err = PTR_ERR(ctx[n]);
+                        goto out_unlock;
+                }
+        }
+
+        for_each_engine(engine, i915, id) {
+                struct i915_request *rq;
+                unsigned long end_time, prime;
+                ktime_t times[2] = {};
+
+                times[0] = ktime_get_raw();
+                for (n = 0; n < nctx; n++) {
+                        rq = i915_request_alloc(engine, ctx[n]);
+                        if (IS_ERR(rq)) {
+                                err = PTR_ERR(rq);
+                                goto out_unlock;
+                        }
+                        i915_request_add(rq);
+                }
+                if (i915_request_wait(rq,
+                                      I915_WAIT_LOCKED,
+                                      HZ / 5) < 0) {
+                        pr_err("Failed to populated %d contexts\n", nctx);
+                        i915_gem_set_wedged(i915);
+                        err = -EIO;
+                        goto out_unlock;
+                }
+
+                times[1] = ktime_get_raw();
+
+                pr_info("Populated %d contexts on %s in %lluns\n",
+                        nctx, engine->name, ktime_to_ns(times[1] - times[0]));
+
+                err = begin_live_test(&t, i915, __func__, engine->name);
+                if (err)
+                        goto out_unlock;
+
+                end_time = jiffies + i915_selftest.timeout_jiffies;
+                for_each_prime_number_from(prime, 2, 8192) {
+                        times[1] = ktime_get_raw();
+
+                        for (n = 0; n < prime; n++) {
+                                rq = i915_request_alloc(engine, ctx[n % nctx]);
+                                if (IS_ERR(rq)) {
+                                        err = PTR_ERR(rq);
+                                        goto out_unlock;
+                                }
+
+                                /*
+                                 * This space is left intentionally blank.
+                                 *
+                                 * We do not actually want to perform any
+                                 * action with this request, we just want
+                                 * to measure the latency in allocation
+                                 * and submission of our breadcrumbs -
+                                 * ensuring that the bare request is sufficient
+                                 * for the system to work (i.e. proper HEAD
+                                 * tracking of the rings, interrupt handling,
+                                 * etc). It also gives us the lowest bounds
+                                 * for latency.
+                                 */
+
+                                i915_request_add(rq);
+                        }
+                        if (i915_request_wait(rq,
+                                              I915_WAIT_LOCKED,
+                                              HZ / 5) < 0) {
+                                pr_err("Switching between %ld contexts timed out\n",
+                                       prime);
+                                i915_gem_set_wedged(i915);
+                                break;
+                        }
+
+                        times[1] = ktime_sub(ktime_get_raw(), times[1]);
+                        if (prime == 2)
+                                times[0] = times[1];
+
+                        if (__igt_timeout(end_time, NULL))
+                                break;
+                }
+
+                err = end_live_test(&t);
+                if (err)
+                        goto out_unlock;
+
+                pr_info("Switch latencies on %s: 1 = %lluns, %lu = %lluns\n",
+                        engine->name,
+                        ktime_to_ns(times[0]),
+                        prime - 1, div64_u64(ktime_to_ns(times[1]), prime - 1));
+        }
+
+out_unlock:
+        mutex_unlock(&i915->drm.struct_mutex);
+        mock_file_free(i915, file);
+        return err;
+}
+
 static struct i915_vma *
 gpu_fill_dw(struct i915_vma *vma, u64 offset, unsigned long count, u32 value)
 {
@@ -714,6 +908,7 @@ int i915_gem_context_live_selftests(struct drm_i915_private *dev_priv)
 {
         static const struct i915_subtest tests[] = {
                 SUBTEST(igt_switch_to_kernel_context),
+                SUBTEST(live_nop_switch),
                 SUBTEST(igt_ctx_exec),
                 SUBTEST(igt_ctx_readonly),
         };