[Intel-gfx] [PATCH] drm/i915: Be more gentle with exiting non-persistent context
Tvrtko Ursulin
tvrtko.ursulin at linux.intel.com
Fri Apr 30 13:27:31 UTC 2021
On 30/04/2021 12:48, Daniel Vetter wrote:
> On Thu, Apr 29, 2021 at 10:46:40AM +0100, Tvrtko Ursulin wrote:
>> From: Tvrtko Ursulin <tvrtko.ursulin at 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.
>
> Can you pls explain here why this is preferrable?
I think there's always the risk of an innocent request getting axed with
preempt to busy being very asynchronous and also engine reset can
sometimes fail as well.
>> To achieve this the patch splits handling of banned contexts from simply
>> exited 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.
>
> Same here, a bit more detail on what exactly was the problem to be fixed
> is needed.
It is a bit multi-faceted. Start with how in some cultures errors
messages are much bigger error flags than in others and much more
difficult to hand-wave "oh that's not a problem really". The the
previous considerations about why not avoid engine reset if we can. Add
on top how non-persistent context exiting is not really an error worthy
of a reset, *if* it exits cleanly reasonably quickly.
You could say make it clean up for itself before it exits, not a kernel
problem. But on the balance of everything, to me it sounds saleable to
just give it some longer time compared to banned contexts, which are the
unquestionably naughty/dangerous ones. Also, how fast non-persistent
contexts will be cleaned up hasn't been defined really. As long as 15ms
is an order of magnitude, plus some, shorter than the normal preempt
timeout I think it is fine.
Regards,
Tvrtko
P.S. Otherwise I plan to respin v2 with consolidated CONTEXT_SCHEDULABLE
flag so fast paths do not have to do too many individual checks.
> -Daniel
>
>>
>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>> Cc: Chris Wilson <chris at chris-wilson.co.uk>
>> Cc: Zhen Han <zhen.han at intel.com>
>> ---
>> drivers/gpu/drm/i915/gem/i915_gem_context.c | 15 +++++++++------
>> 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 | 12 ++++++++++--
>> drivers/gpu/drm/i915/i915_request.c | 2 +-
>> 5 files changed, 38 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c b/drivers/gpu/drm/i915/gem/i915_gem_context.c
>> index fd8ee52e17a4..5a6eba1232cd 100644
>> --- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
>> @@ -426,7 +426,8 @@ 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;
>> @@ -443,6 +444,8 @@ static void kill_engines(struct i915_gem_engines *engines, bool ban)
>>
>> if (ban && intel_context_set_banned(ce))
>> continue;
>> + else if (!persistent && intel_context_set_non_persistent(ce))
>> + continue;
>>
>> /*
>> * Check the current active state of this context; if we
>> @@ -454,7 +457,7 @@ 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
>> @@ -466,8 +469,6 @@ 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);
>> @@ -480,7 +481,8 @@ 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));
>> @@ -526,7 +528,8 @@ 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.h b/drivers/gpu/drm/i915/gt/intel_context.h
>> index f83a73a2b39f..b0e812b8ce39 100644
>> --- a/drivers/gpu/drm/i915/gt/intel_context.h
>> +++ b/drivers/gpu/drm/i915/gt/intel_context.h
>> @@ -220,6 +220,23 @@ static inline bool intel_context_set_banned(struct intel_context *ce)
>> return test_and_set_bit(CONTEXT_BANNED, &ce->flags);
>> }
>>
>> +static inline bool intel_context_is_non_persistent(const struct intel_context *ce)
>> +{
>> + return test_bit(CONTEXT_NON_PERSISTENT, &ce->flags);
>> +}
>> +
>> +static inline bool intel_context_set_non_persistent(struct intel_context *ce)
>> +{
>> + return test_and_set_bit(CONTEXT_NON_PERSISTENT, &ce->flags);
>> +}
>> +
>> +static inline bool intel_context_is_schedulable(const struct intel_context *ce)
>> +{
>> + return !intel_context_is_banned(ce) &&
>> + !(intel_context_is_closed(ce) &&
>> + intel_context_is_non_persistent(ce));
>> +}
>> +
>> static inline bool
>> intel_context_force_single_submission(const 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 ed8c447a7346..aa949c539e93 100644
>> --- a/drivers/gpu/drm/i915/gt/intel_context_types.h
>> +++ b/drivers/gpu/drm/i915/gt/intel_context_types.h
>> @@ -95,6 +95,7 @@ struct intel_context {
>> #define CONTEXT_BANNED 6
>> #define CONTEXT_FORCE_SINGLE_SUBMISSION 7
>> #define CONTEXT_NOPREEMPT 8
>> +#define CONTEXT_NON_PERSISTENT 9 /* Only if also 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 de124870af44..5ad7272fbbc4 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))
>> @@ -1204,12 +1204,20 @@ 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_closed(ce) &&
>> + intel_context_is_non_persistent(ce)))
>> + return 15;
>>
>> return READ_ONCE(engine->props.preempt_timeout_ms);
>> }
>> diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
>> index bec9c3652188..bbac87535923 100644
>> --- a/drivers/gpu/drm/i915/i915_request.c
>> +++ b/drivers/gpu/drm/i915/i915_request.c
>> @@ -660,7 +660,7 @@ 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
>>
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>
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