[Intel-gfx] [PATCH v2] drm/i915/gt: Transfer old virtual breadcrumbs to irq_worker
Tvrtko Ursulin
tvrtko.ursulin at linux.intel.com
Tue May 12 15:17:30 UTC 2020
On 12/05/2020 14:22, Chris Wilson wrote:
> The second try at staging the transfer of the breadcrumb. In part one,
> we realised we could not simply move to the second engine as we were
> only holding the breadcrumb lock on the first. So in commit 6c81e21a4742
> ("drm/i915/gt: Stage the transfer of the virtual breadcrumb"), we
> removed it from the first engine and marked up this request to reattach
> the signaling on the new engine. However, this failed to take into
> account that we only attach the breadcrumb if the new request is added
> at the start of the queue, which if we are transferring, it is because
> we know there to be a request to be signaled (and hence we would not be
> attached).
>
> In this attempt, we try to transfer the completed requests to the
> irq_worker on its rq->engine->breadcrumbs. This preserves the coupling
> between the rq and its breadcrumbs, so that
> i915_request_cancel_breadcrumb() does not attempt to manipulate the list
> under the wrong lock.
>
> Fixes: 6c81e21a4742 ("drm/i915/gt: Stage the transfer of the virtual breadcrumb")
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> ---
> v2: rewrite from scratch with a new idea
> ---
> drivers/gpu/drm/i915/gt/intel_breadcrumbs.c | 33 ++++++++++++++++++++
> drivers/gpu/drm/i915/gt/intel_engine.h | 3 ++
> drivers/gpu/drm/i915/gt/intel_engine_types.h | 2 ++
> drivers/gpu/drm/i915/gt/intel_lrc.c | 26 ++-------------
> 4 files changed, 41 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
> index cbedba857d43..e09dc162b508 100644
> --- a/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
> +++ b/drivers/gpu/drm/i915/gt/intel_breadcrumbs.c
> @@ -155,6 +155,8 @@ static void signal_irq_work(struct irq_work *work)
> if (b->irq_armed && list_empty(&b->signalers))
> __intel_breadcrumbs_disarm_irq(b);
>
> + list_splice_init(&b->signaled_requests, &signal);
> +
> list_for_each_entry_safe(ce, cn, &b->signalers, signal_link) {
> GEM_BUG_ON(list_empty(&ce->signals));
>
> @@ -255,6 +257,7 @@ void intel_engine_init_breadcrumbs(struct intel_engine_cs *engine)
>
> spin_lock_init(&b->irq_lock);
> INIT_LIST_HEAD(&b->signalers);
> + INIT_LIST_HEAD(&b->signaled_requests);
>
> init_irq_work(&b->irq_work, signal_irq_work);
> }
> @@ -274,6 +277,36 @@ void intel_engine_reset_breadcrumbs(struct intel_engine_cs *engine)
> spin_unlock_irqrestore(&b->irq_lock, flags);
> }
>
> +void intel_engine_transfer_breadcrumbs(struct intel_engine_cs *engine,
> + struct intel_context *ce)
> +{
> + struct intel_breadcrumbs *b = &engine->breadcrumbs;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&b->irq_lock, flags);
> + if (!list_empty(&ce->signals)) {
> + struct i915_request *rq, *next;
> +
> + list_for_each_entry_safe(rq, next, &ce->signals, signal_link) {
> + GEM_BUG_ON(rq->engine != engine);
> + GEM_BUG_ON(!i915_request_completed(rq));
Do you remember why the breadcrumbs code uses local __request_completed
helper?
From here vvv
> +
> + clear_bit(I915_FENCE_FLAG_SIGNAL, &rq->fence.flags);
> + if (!__dma_fence_signal(&rq->fence))
> + continue;
> +
> + i915_request_get(rq);
> + list_add_tail(&rq->signal_link, &b->signaled_requests);
^^^ to here looks like a block which could be shared with signal_irq_work.
> + }
> +
> + INIT_LIST_HEAD(&ce->signals);
Hm because list_add and not list_move you can't assert all have been
unlinked.
> + list_del_init(&ce->signal_link);
> +
> + irq_work_queue(&b->irq_work);
> + }
> + spin_unlock_irqrestore(&b->irq_lock, flags);
> +}
> +
> void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine)
> {
> }
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine.h b/drivers/gpu/drm/i915/gt/intel_engine.h
> index cb789c8bf06b..45418f887953 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine.h
> +++ b/drivers/gpu/drm/i915/gt/intel_engine.h
> @@ -238,6 +238,9 @@ intel_engine_signal_breadcrumbs(struct intel_engine_cs *engine)
> void intel_engine_reset_breadcrumbs(struct intel_engine_cs *engine);
> void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine);
>
> +void intel_engine_transfer_breadcrumbs(struct intel_engine_cs *engine,
> + struct intel_context *ce);
> +
> void intel_engine_print_breadcrumbs(struct intel_engine_cs *engine,
> struct drm_printer *p);
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_types.h b/drivers/gpu/drm/i915/gt/intel_engine_types.h
> index c113b7805e65..e20b39eefd79 100644
> --- a/drivers/gpu/drm/i915/gt/intel_engine_types.h
> +++ b/drivers/gpu/drm/i915/gt/intel_engine_types.h
> @@ -377,6 +377,8 @@ struct intel_engine_cs {
> spinlock_t irq_lock;
> struct list_head signalers;
>
> + struct list_head signaled_requests;
> +
> struct irq_work irq_work; /* for use from inside irq_lock */
>
> unsigned int irq_enabled;
> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> index 15716e4d6b76..ac32d494b07d 100644
> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> @@ -1821,30 +1821,10 @@ static bool virtual_matches(const struct virtual_engine *ve,
> return true;
> }
>
> -static void virtual_xfer_breadcrumbs(struct virtual_engine *ve,
> - struct i915_request *rq)
> +static void virtual_xfer_breadcrumbs(struct virtual_engine *ve)
> {
> - struct intel_engine_cs *old = ve->siblings[0];
> -
> /* All unattached (rq->engine == old) must already be completed */
This comments feels a bit out of place now.
> -
> - spin_lock(&old->breadcrumbs.irq_lock);
> - if (!list_empty(&ve->context.signal_link)) {
> - list_del_init(&ve->context.signal_link);
> -
> - /*
> - * We cannot acquire the new engine->breadcrumbs.irq_lock
> - * (as we are holding a breadcrumbs.irq_lock already),
> - * so attach this request to the signaler on submission.
> - * The queued irq_work will occur when we finally drop
> - * the engine->active.lock after dequeue.
> - */
> - set_bit(DMA_FENCE_FLAG_ENABLE_SIGNAL_BIT, &rq->fence.flags);
> -
> - /* Also transfer the pending irq_work for the old breadcrumb. */
> - intel_engine_signal_breadcrumbs(rq->engine);
> - }
> - spin_unlock(&old->breadcrumbs.irq_lock);
> + intel_engine_transfer_breadcrumbs(ve->siblings[0], &ve->context);
But isn't ve->siblings[0] the old engine at this point so new target
engine would have to be explicitly passed in?
> }
>
> #define for_each_waiter(p__, rq__) \
> @@ -2279,7 +2259,7 @@ static void execlists_dequeue(struct intel_engine_cs *engine)
> engine);
>
> if (!list_empty(&ve->context.signals))
> - virtual_xfer_breadcrumbs(ve, rq);
> + virtual_xfer_breadcrumbs(ve);
>
> /*
> * Move the bound engine to the top of the list
>
Regards,
Tvrtko
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