Re: [PATCH 10/40] drm/i915/selftests: Basic stress test for rapid context switching

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> 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
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  .../gpu/drm/i915/selftests/i915_gem_context.c | 188 ++++++++++++++++++
>  1 file changed, 188 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/selftests/i915_gem_context.c b/drivers/gpu/drm/i915/selftests/i915_gem_context.c
> index a89d31075c7a..f1a57e3c3820 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 +34,191 @@
>  
>  #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;

Blunt but should work as we check this for tests
that matter and thus leftovers should not matter.

> +	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;
> +
> +	i915_retire_requests(i915);
> +
> +	if (wait_for(intel_engines_are_idle(i915), 10)) {
> +		pr_err("%s(%s): GPU not idle\n", t->func, t->name);
> +		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);
> +		}
> +		i915_request_wait(rq,
> +				  I915_WAIT_LOCKED,
> +				  MAX_SCHEDULE_TIMEOUT);
> +		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);

We get the breadcrumbs in place, with the wa_tails and so on so this
should work without any nops nor bb ends.

> +			}
> +			i915_request_wait(rq,
> +					  I915_WAIT_LOCKED,
> +					  MAX_SCHEDULE_TIMEOUT);
> +
> +			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)
>  {
> @@ -718,6 +905,7 @@ 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),

Due to the nature of the test, the nop has a minor twist to
think there is a nop in ring. This is more of a nop request,
or empty request. 

'live_bare|empty_switch' ?

Can't think of better so I dont insist, so regardless

Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>

>  		SUBTEST(igt_ctx_exec),
>  		SUBTEST(igt_ctx_readonly),
>  	};
> -- 
> 2.19.0
>
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