Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes:
> Reduce the irq_work llist for attaching the callbacks to the signal for
> both smaller structs (two fewer pointers!) and simpler [debug] code:
>
> Function old new delta
> irq_execute_cb 35 34 -1
> __igt_breadcrumbs_smoketest 1684 1682 -2
> i915_request_retire 2003 1996 -7
> __i915_request_create 1047 1040 -7
> __notify_execute_cb 135 126 -9
> __i915_request_ctor 188 178 -10
> __await_execution.part.constprop 451 440 -11
> igt_wait_request 924 714 -210
>
> One minor artifact is that the order of cb exection is reversed. No
> current use cases are affected by that change.
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_request.c | 18 +++++++++---------
> drivers/gpu/drm/i915/i915_request.h | 2 +-
> 2 files changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> index c282719ad3ac..22df5b229aed 100644
> --- a/drivers/gpu/drm/i915/i915_request.c
> +++ b/drivers/gpu/drm/i915/i915_request.c
> @@ -42,7 +42,6 @@
> #include "intel_pm.h"
>
> struct execute_cb {
> - struct list_head link;
> struct irq_work work;
> struct i915_sw_fence *fence;
> void (*hook)(struct i915_request *rq, struct dma_fence *signal);
> @@ -189,14 +188,14 @@ static void irq_execute_cb_hook(struct irq_work *wrk)
>
> static void __notify_execute_cb(struct i915_request *rq)
> {
> - struct execute_cb *cb;
> + struct execute_cb *cb, *cn;
>
> lockdep_assert_held(&rq->lock);
>
> - if (list_empty(&rq->execute_cb))
> + if (llist_empty(&rq->execute_cb))
> return;
>
> - list_for_each_entry(cb, &rq->execute_cb, link)
> + llist_for_each_entry_safe(cb, cn, rq->execute_cb.first, work.llnode)
> irq_work_queue(&cb->work);
>
> /*
> @@ -209,7 +208,7 @@ static void __notify_execute_cb(struct i915_request *rq)
> * preempt-to-idle cycle on the target engine, all the while the
> * master execute_cb may refire.
> */
> - INIT_LIST_HEAD(&rq->execute_cb);
> + rq->execute_cb.first = NULL;
> }
>
> static inline void
> @@ -327,7 +326,7 @@ bool i915_request_retire(struct i915_request *rq)
> set_bit(I915_FENCE_FLAG_ACTIVE, &rq->fence.flags);
> __notify_execute_cb(rq);
> }
> - GEM_BUG_ON(!list_empty(&rq->execute_cb));
> + GEM_BUG_ON(!llist_empty(&rq->execute_cb));
> spin_unlock_irq(&rq->lock);
>
> remove_from_client(rq);
> @@ -395,7 +394,8 @@ __await_execution(struct i915_request *rq,
> i915_sw_fence_complete(cb->fence);
> kmem_cache_free(global.slab_execute_cbs, cb);
> } else {
> - list_add_tail(&cb->link, &signal->execute_cb);
> + cb->work.llnode.next = signal->execute_cb.first;
> + signal->execute_cb.first = &cb->work.llnode;
With this part giving more glues as of why can we do this,
Reviewed-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> }
> spin_unlock_irq(&signal->lock);
>
> @@ -704,7 +704,7 @@ static void __i915_request_ctor(void *arg)
> rq->file_priv = NULL;
> rq->capture_list = NULL;
>
> - INIT_LIST_HEAD(&rq->execute_cb);
> + init_llist_head(&rq->execute_cb);
> }
>
> struct i915_request *
> @@ -794,7 +794,7 @@ __i915_request_create(struct intel_context *ce, gfp_t gfp)
> rq->batch = NULL;
> GEM_BUG_ON(rq->file_priv);
> GEM_BUG_ON(rq->capture_list);
> - GEM_BUG_ON(!list_empty(&rq->execute_cb));
> + GEM_BUG_ON(!llist_empty(&rq->execute_cb));
>
> /*
> * Reserve space in the ring buffer for all the commands required to
> diff --git a/drivers/gpu/drm/i915/i915_request.h b/drivers/gpu/drm/i915/i915_request.h
> index 8ec7ee4dbadc..5d4709a3dace 100644
> --- a/drivers/gpu/drm/i915/i915_request.h
> +++ b/drivers/gpu/drm/i915/i915_request.h
> @@ -214,7 +214,7 @@ struct i915_request {
> ktime_t emitted;
> } duration;
> };
> - struct list_head execute_cb;
> + struct llist_head execute_cb;
> struct i915_sw_fence semaphore;
>
> /*
> --
> 2.20.1
>
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> Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
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