On Mon, Mar 26, 2018 at 12:50:41PM +0100, Chris Wilson wrote:
> Install a timer when trying to preempt on behalf of an important
> context such that if the active context does not honour the preemption
> request within the desired timeout, then we reset the GPU to allow the
> important context to run.
>
> (Open: should not the timer be started from receiving the high priority
> request...)
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/intel_lrc.c | 53 +++++++++++++++++++++++++++++++++
> drivers/gpu/drm/i915/intel_ringbuffer.h | 8 +++++
> 2 files changed, 61 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 50688fc889d9..6da816d23cb3 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -533,6 +533,47 @@ static void inject_preempt_context(struct intel_engine_cs *engine)
>
> execlists_clear_active(execlists, EXECLISTS_ACTIVE_HWACK);
> execlists_set_active(execlists, EXECLISTS_ACTIVE_PREEMPT);
> +
> + /* Set a timer to force preemption vs hostile userspace */
> + if (execlists->queue_preempt_timeout) {
> + GEM_TRACE("%s timeout=%uns\n",
> + engine->name, execlists->queue_preempt_timeout);
> + hrtimer_start(&execlists->preempt_timer,
> + ktime_set(0, execlists->queue_preempt_timeout),
> + HRTIMER_MODE_REL);
> + }
> +}
> +
> +static enum hrtimer_restart preempt_timeout(struct hrtimer *hrtimer)
> +{
> + struct intel_engine_execlists *execlists =
> + container_of(hrtimer, typeof(*execlists), preempt_timer);
> +
> + GEM_TRACE("%s\n",
> + container_of(execlists,
> + struct intel_engine_cs,
> + execlists)->name);
> +
> + queue_work(system_highpri_wq, &execlists->preempt_reset);
> + return HRTIMER_NORESTART;
> +}
> +
> +static void preempt_reset(struct work_struct *work)
> +{
> + struct intel_engine_cs *engine =
> + container_of(work, typeof(*engine), execlists.preempt_reset);
> +
> + GEM_TRACE("%s\n", engine->name);
> +
> + tasklet_disable(&engine->execlists.tasklet);
> +
> + engine->execlists.tasklet.func(engine->execlists.tasklet.data);
This seems redundant with the execlists_reset_prepare already doing a process_csb
at a later time to decide whether to execute or abort the reset. In your
previous proposal you suggested tasklet disable and kill here.
> +
> + if (execlists_is_active(&engine->execlists, EXECLISTS_ACTIVE_PREEMPT))
> + i915_handle_error(engine->i915, BIT(engine->id), 0,
> + "preemption timed out on %s", engine->name);
> +
> + tasklet_enable(&engine->execlists.tasklet);
> }
>
> static void complete_preempt_context(struct intel_engine_execlists *execlists)
> @@ -542,6 +583,10 @@ static void complete_preempt_context(struct intel_engine_execlists *execlists)
> execlists_cancel_port_requests(execlists);
> execlists_unwind_incomplete_requests(execlists);
>
> + /* If the timer already fired, complete the reset */
> + if (hrtimer_try_to_cancel(&execlists->preempt_timer) < 0)
> + return;
> +
> execlists_clear_active(execlists, EXECLISTS_ACTIVE_PREEMPT);
> }
>
> @@ -708,6 +753,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> kmem_cache_free(engine->i915->priorities, p);
> }
> done:
> + execlists->queue_preempt_timeout = 0; /* preemption point passed */
> execlists->queue_priority = rb ? to_priolist(rb)->priority : INT_MIN;
> execlists->first = rb;
> if (submit)
> @@ -864,6 +910,7 @@ static void execlists_cancel_requests(struct intel_engine_cs *engine)
>
> /* Remaining _unready_ requests will be nop'ed when submitted */
>
> + execlists->queue_preempt_timeout = 0;
> execlists->queue_priority = INT_MIN;
> execlists->queue = RB_ROOT;
> execlists->first = NULL;
> @@ -1080,6 +1127,7 @@ static void queue_request(struct intel_engine_cs *engine,
> static void __submit_queue(struct intel_engine_cs *engine, int prio)
> {
> engine->execlists.queue_priority = prio;
> + engine->execlists.queue_preempt_timeout = 0;
> tasklet_hi_schedule(&engine->execlists.tasklet);
> }
>
> @@ -2270,6 +2318,11 @@ logical_ring_setup(struct intel_engine_cs *engine)
> tasklet_init(&engine->execlists.tasklet,
> execlists_submission_tasklet, (unsigned long)engine);
>
> + INIT_WORK(&engine->execlists.preempt_reset, preempt_reset);
> + hrtimer_init(&engine->execlists.preempt_timer,
> + CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> + engine->execlists.preempt_timer.function = preempt_timeout;
> +
> logical_ring_default_vfuncs(engine);
> logical_ring_default_irqs(engine);
> }
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
> index 4c71dcdc722b..7166f47c8489 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.h
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
> @@ -284,6 +284,11 @@ struct intel_engine_execlists {
> */
> int queue_priority;
>
> + /**
> + * @queue_preempt_timeout: Timeout in ns before forcing preemption.
> + */
> + unsigned int queue_preempt_timeout;
> +
> /**
> * @queue: queue of requests, in priority lists
> */
> @@ -313,6 +318,9 @@ struct intel_engine_execlists {
> * @preempt_complete_status: expected CSB upon completing preemption
> */
> u32 preempt_complete_status;
> +
> + struct hrtimer preempt_timer;
> + struct work_struct preempt_reset;
> };
>
> #define INTEL_ENGINE_CS_MAX_NAME 8
> --
> 2.16.3
>
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