Re: [Intel-gfx] [PATCH] drm/i915: Be more gentle when exiting non-persistent contexts

Matthew Brost
2021-08-05T16:32:21Z

On Thu, Aug 05, 2021 at 01:05:09PM +0100, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>
> When a non-persistent context exits we currently mark it as banned in
> order to trigger fast termination of any outstanding GPU jobs it may have
> left running.
>
> In doing so we apply a very strict 1ms limit in which the left over job
> has to preempt before we issues an engine resets.
>
> Some workloads are not able to cleanly preempt in that time window and it
> can be argued that it would instead be better to give them a bit more
> grace since avoiding engine resets is generally preferrable.
>
> To achieve this the patch splits handling of banned contexts from simply
> closed non-persistent ones and then applies different timeouts for both
> and also extends the criteria which determines if a request should be
> scheduled back in after preemption or not.
>
> 15ms preempt timeout grace is given to exited non-persistent contexts
> which have been empirically tested to satisfy customers requirements
> and still provides reasonably quick cleanup post exit.
>

I think you need to rework your thinking here a bit as this a very
execlists specific solution and the GuC needs to be considered.

> v2:
> * Streamline fast path checks.
>
> v3:
> * Simplify by using only schedulable status.
> * Increase timeout to 20ms.
>
> v4:
> * Fix live_execlists selftest.
>
> v5:
> * Fix logic in kill_engines.
>
> v6:
> * Rebase.
>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Zhen Han <zhen.han@intel.com>
> ---
> drivers/gpu/drm/i915/gem/i915_gem_context.c | 22 +++++++++++++------
> drivers/gpu/drm/i915/gt/intel_context.c | 2 ++
> drivers/gpu/drm/i915/gt/intel_context.h | 17 +++++++++++++-
> drivers/gpu/drm/i915/gt/intel_context_types.h | 1 +
> .../drm/i915/gt/intel_execlists_submission.c | 11 ++++++++--
> drivers/gpu/drm/i915/gt/selftest_execlists.c | 20 +++++++++++------
> drivers/gpu/drm/i915/i915_request.c | 2 +-
> 7 files changed, 57 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> index cff72679ad7c..21fe5d4057ab 100644
> --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
> @@ -1065,7 +1065,8 @@ static struct intel_engine_cs *active_engine(struct intel_context *ce)
> return engine;
> }
>
> -static void kill_engines(struct i915_gem_engines *engines, bool ban)
> +static void
> +kill_engines(struct i915_gem_engines *engines, bool ban, bool persistent)
> {
> struct i915_gem_engines_iter it;
> struct intel_context *ce;
> @@ -1079,8 +1080,15 @@ static void kill_engines(struct i915_gem_engines *engines, bool ban)
> */
> for_each_gem_engine(ce, engines, it) {
> struct intel_engine_cs *engine;
> + bool skip = false;
> +
> + if (ban)
> + skip = intel_context_ban(ce, NULL);
> + else if (!persistent)
> + skip = !intel_context_clear_schedulable(ce);

schedulable doesn't hook into the backend at all, while
intel_context_ban does. In the case of GuC submission intel_context_ban
changes to preemption timeout to 1 us and disables scheduling resulting
in the context getting kicked off the hardware immediately. You likely
need to update intel_context_clear_schedulable to use the same vfunc as
intel_context_ban() but accept an argument for the value of the
preemption timeout. For a ban user a lower value, for clearing
schedulable use a higher value.

>
> - if (ban && intel_context_ban(ce, NULL))
> + /* Already previously banned or made non-schedulable? */
> + if (skip)
> continue;
>
> /*
> @@ -1093,7 +1101,7 @@ static void kill_engines(struct i915_gem_engines *engines, bool ban)
> engine = active_engine(ce);
>
> /* First attempt to gracefully cancel the context */
> - if (engine && !__cancel_engine(engine) && ban)
> + if (engine && !__cancel_engine(engine) && (ban || !persistent))
> /*
> * If we are unable to send a preemptive pulse to bump
> * the context from the GPU, we have to resort to a full
> @@ -1105,8 +1113,6 @@ static void kill_engines(struct i915_gem_engines *engines, bool ban)
>
> static void kill_context(struct i915_gem_context *ctx)
> {
> - bool ban = (!i915_gem_context_is_persistent(ctx) ||
> - !ctx->i915->params.enable_hangcheck);
> struct i915_gem_engines *pos, *next;
>
> spin_lock_irq(&ctx->stale.lock);
> @@ -1119,7 +1125,8 @@ static void kill_context(struct i915_gem_context *ctx)
>
> spin_unlock_irq(&ctx->stale.lock);
>
> - kill_engines(pos, ban);
> + kill_engines(pos, !ctx->i915->params.enable_hangcheck,
> + i915_gem_context_is_persistent(ctx));
>
> spin_lock_irq(&ctx->stale.lock);
> GEM_BUG_ON(i915_sw_fence_signaled(&pos->fence));
> @@ -1165,7 +1172,8 @@ static void engines_idle_release(struct i915_gem_context *ctx,
>
> kill:
> if (list_empty(&engines->link)) /* raced, already closed */
> - kill_engines(engines, true);
> + kill_engines(engines, true,
> + i915_gem_context_is_persistent(ctx));
>
> i915_sw_fence_commit(&engines->fence);
> }
> diff --git a/drivers/gpu/drm/i915/gt/intel_context.c b/drivers/gpu/drm/i915/gt/intel_context.c
> index 745e84c72c90..bc1701ef1578 100644
> --- a/drivers/gpu/drm/i915/gt/intel_context.c
> +++ b/drivers/gpu/drm/i915/gt/intel_context.c
> @@ -382,6 +382,8 @@ intel_context_init(struct intel_context *ce, struct intel_engine_cs *engine)
> ce->ring = NULL;
> ce->ring_size = SZ_4K;
>
> + __set_bit(CONTEXT_SCHEDULABLE, &ce->flags);
> +
> ewma_runtime_init(&ce->runtime.avg);
>
> ce->vm = i915_vm_get(engine->gt->vm);
> diff --git a/drivers/gpu/drm/i915/gt/intel_context.h b/drivers/gpu/drm/i915/gt/intel_context.h
> index c41098950746..5b50716654dd 100644
> --- a/drivers/gpu/drm/i915/gt/intel_context.h
> +++ b/drivers/gpu/drm/i915/gt/intel_context.h
> @@ -251,7 +251,22 @@ static inline bool intel_context_is_banned(const struct intel_context *ce)
>
> static inline bool intel_context_set_banned(struct intel_context *ce)
> {
> - return test_and_set_bit(CONTEXT_BANNED, &ce->flags);
> + bool banned = test_and_set_bit(CONTEXT_BANNED, &ce->flags);
> +
> + if (!banned)
> + clear_bit(CONTEXT_SCHEDULABLE, &ce->flags);
> +
> + return banned;
> +}
> +
> +static inline bool intel_context_clear_schedulable(struct intel_context *ce)
> +{
> + return test_and_clear_bit(CONTEXT_SCHEDULABLE, &ce->flags);
> +}
> +
> +static inline bool intel_context_is_schedulable(const struct intel_context *ce)
> +{
> + return test_bit(CONTEXT_SCHEDULABLE, &ce->flags);
> }
>
> static inline bool intel_context_ban(struct intel_context *ce,
> diff --git a/drivers/gpu/drm/i915/gt/intel_context_types.h b/drivers/gpu/drm/i915/gt/intel_context_types.h
> index e54351a170e2..3306c70c9c54 100644
> --- a/drivers/gpu/drm/i915/gt/intel_context_types.h
> +++ b/drivers/gpu/drm/i915/gt/intel_context_types.h
> @@ -112,6 +112,7 @@ struct intel_context {
> #define CONTEXT_FORCE_SINGLE_SUBMISSION 7
> #define CONTEXT_NOPREEMPT 8
> #define CONTEXT_LRCA_DIRTY 9
> +#define CONTEXT_SCHEDULABLE 10 /* Unless banned or non-persistent closed. */
>
> struct {
> u64 timeout_us;
> diff --git a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> index de5f9c86b9a4..778f3cda3c71 100644
> --- a/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> +++ b/drivers/gpu/drm/i915/gt/intel_execlists_submission.c
> @@ -478,7 +478,7 @@ __execlists_schedule_in(struct i915_request *rq)
> !intel_engine_has_heartbeat(engine)))
> intel_context_set_banned(ce);
>
> - if (unlikely(intel_context_is_banned(ce) || bad_request(rq)))
> + if (unlikely(!intel_context_is_schedulable(ce) || bad_request(rq)))
> reset_active(rq, engine);
>
> if (IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM))
> @@ -1222,12 +1222,19 @@ static void record_preemption(struct intel_engine_execlists *execlists)
> static unsigned long active_preempt_timeout(struct intel_engine_cs *engine,
> const struct i915_request *rq)
> {
> + struct intel_context *ce;
> +
> if (!rq)
> return 0;
>
> + ce = rq->context;
> +
> /* Force a fast reset for terminated contexts (ignoring sysfs!) */
> - if (unlikely(intel_context_is_banned(rq->context) || bad_request(rq)))
> + if (unlikely(intel_context_is_banned(ce) || bad_request(rq)))
> return 1;
> + /* Longer grace for closed non-persistent contexts to avoid resets. */
> + else if (unlikely(!intel_context_is_schedulable(ce)))
> + return 20;

Likely want a define for '1' and '20' too.

Matt

>
> return READ_ONCE(engine->props.preempt_timeout_ms);
> }
> diff --git a/drivers/gpu/drm/i915/gt/selftest_execlists.c b/drivers/gpu/drm/i915/gt/selftest_execlists.c
> index f12ffe797639..da36c015caf4 100644
> --- a/drivers/gpu/drm/i915/gt/selftest_execlists.c
> +++ b/drivers/gpu/drm/i915/gt/selftest_execlists.c
> @@ -2050,6 +2050,12 @@ struct live_preempt_cancel {
> struct preempt_client a, b;
> };
>
> +static void context_clear_banned(struct intel_context *ce)
> +{
> + clear_bit(CONTEXT_BANNED, &ce->flags);
> + set_bit(CONTEXT_SCHEDULABLE, &ce->flags);
> +}
> +
> static int __cancel_active0(struct live_preempt_cancel *arg)
> {
> struct i915_request *rq;
> @@ -2068,7 +2074,7 @@ static int __cancel_active0(struct live_preempt_cancel *arg)
> if (IS_ERR(rq))
> return PTR_ERR(rq);
>
> - clear_bit(CONTEXT_BANNED, &rq->context->flags);
> + context_clear_banned(rq->context);
> i915_request_get(rq);
> i915_request_add(rq);
> if (!igt_wait_for_spinner(&arg->a.spin, rq)) {
> @@ -2112,7 +2118,7 @@ static int __cancel_active1(struct live_preempt_cancel *arg)
> if (IS_ERR(rq[0]))
> return PTR_ERR(rq[0]);
>
> - clear_bit(CONTEXT_BANNED, &rq[0]->context->flags);
> + context_clear_banned(rq[0]->context);
> i915_request_get(rq[0]);
> i915_request_add(rq[0]);
> if (!igt_wait_for_spinner(&arg->a.spin, rq[0])) {
> @@ -2128,7 +2134,7 @@ static int __cancel_active1(struct live_preempt_cancel *arg)
> goto out;
> }
>
> - clear_bit(CONTEXT_BANNED, &rq[1]->context->flags);
> + context_clear_banned(rq[1]->context);
> i915_request_get(rq[1]);
> err = i915_request_await_dma_fence(rq[1], &rq[0]->fence);
> i915_request_add(rq[1]);
> @@ -2183,7 +2189,7 @@ static int __cancel_queued(struct live_preempt_cancel *arg)
> if (IS_ERR(rq[0]))
> return PTR_ERR(rq[0]);
>
> - clear_bit(CONTEXT_BANNED, &rq[0]->context->flags);
> + context_clear_banned(rq[0]->context);
> i915_request_get(rq[0]);
> i915_request_add(rq[0]);
> if (!igt_wait_for_spinner(&arg->a.spin, rq[0])) {
> @@ -2197,7 +2203,7 @@ static int __cancel_queued(struct live_preempt_cancel *arg)
> goto out;
> }
>
> - clear_bit(CONTEXT_BANNED, &rq[1]->context->flags);
> + context_clear_banned(rq[1]->context);
> i915_request_get(rq[1]);
> err = i915_request_await_dma_fence(rq[1], &rq[0]->fence);
> i915_request_add(rq[1]);
> @@ -2273,7 +2279,7 @@ static int __cancel_hostile(struct live_preempt_cancel *arg)
> if (IS_ERR(rq))
> return PTR_ERR(rq);
>
> - clear_bit(CONTEXT_BANNED, &rq->context->flags);
> + context_clear_banned(rq->context);
> i915_request_get(rq);
> i915_request_add(rq);
> if (!igt_wait_for_spinner(&arg->a.spin, rq)) {
> @@ -2329,7 +2335,7 @@ static int __cancel_fail(struct live_preempt_cancel *arg)
> if (IS_ERR(rq))
> return PTR_ERR(rq);
>
> - clear_bit(CONTEXT_BANNED, &rq->context->flags);
> + context_clear_banned(rq->context);
> i915_request_get(rq);
> i915_request_add(rq);
> if (!igt_wait_for_spinner(&arg->a.spin, rq)) {
> diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> index ce446716d092..b1a9bec83339 100644
> --- a/drivers/gpu/drm/i915/i915_request.c
> +++ b/drivers/gpu/drm/i915/i915_request.c
> @@ -583,7 +583,7 @@ bool __i915_request_submit(struct i915_request *request)
> goto active;
> }
>
> - if (unlikely(intel_context_is_banned(request->context)))
> + if (unlikely(!intel_context_is_schedulable(request->context)))
> i915_request_set_error_once(request, -EIO);
>
> if (unlikely(fatal_error(request->fence.error)))
> --
> 2.30.2
>