Re: [PATCH 30/43] drm/i915/bdw: Two-stage execlist submit process

Daniel, Thomas
2014-08-15T08:51:27Z

> -----Original Message-----
> From: Daniel Vetter [mailto:daniel.vetter@ffwll.ch] On Behalf Of Daniel
> Vetter
> Sent: Thursday, August 14, 2014 9:10 PM
> To: Daniel, Thomas
> Cc: intel-gfx@lists.freedesktop.org
> Subject: Re: [Intel-gfx] [PATCH 30/43] drm/i915/bdw: Two-stage execlist
> submit process
>
> On Thu, Jul 24, 2014 at 05:04:38PM +0100, Thomas Daniel wrote:
> > From: Michel Thierry <michel.thierry@intel.com>
> >
> > Context switch (and execlist submission) should happen only when other
> > contexts are not active, otherwise pre-emption occurs.
> >
> > To assure this, we place context switch requests in a queue and those
> > request are later consumed when the right context switch interrupt is
> > received (still TODO).
> >
> > v2: Use a spinlock, do not remove the requests on unqueue (wait for
> > context switch completion).
> >
> > Signed-off-by: Thomas Daniel <thomas.daniel@intel.com>
> >
> > v3: Several rebases and code changes. Use unique ID.
> >
> > v4:
> > - Move the queue/lock init to the late ring initialization.
> > - Damien's kmalloc review comments: check return, use sizeof(*req), do
> > not cast.
> >
> > v5:
> > - Do not reuse drm_i915_gem_request. Instead, create our own.
> > - New namespace.
> >
> > Signed-off-by: Michel Thierry <michel.thierry@intel.com> (v1)
> > Signed-off-by: Oscar Mateo <oscar.mateo@intel.com> (v2-v5)
> > ---
> > drivers/gpu/drm/i915/intel_lrc.c | 63
> ++++++++++++++++++++++++++++++-
> > drivers/gpu/drm/i915/intel_lrc.h | 8 ++++
> > drivers/gpu/drm/i915/intel_ringbuffer.h | 2 +
> > 3 files changed, 71 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_lrc.c
> > b/drivers/gpu/drm/i915/intel_lrc.c
> > index 5b6f416..9e91169 100644
> > --- a/drivers/gpu/drm/i915/intel_lrc.c
> > +++ b/drivers/gpu/drm/i915/intel_lrc.c
> > @@ -217,6 +217,63 @@ static int execlists_submit_context(struct
> intel_engine_cs *ring,
> > return 0;
> > }
> >
> > +static void execlists_context_unqueue(struct intel_engine_cs *ring) {
> > + struct intel_ctx_submit_request *req0 = NULL, *req1 = NULL;
> > + struct intel_ctx_submit_request *cursor = NULL, *tmp = NULL;
> > +
> > + if (list_empty(&ring->execlist_queue))
> > + return;
> > +
> > + /* Try to read in pairs */
> > + list_for_each_entry_safe(cursor, tmp, &ring->execlist_queue,
> > +execlist_link) {
>
> Ok, because checkpatch I've looked at this. Imo open-coding this would be
> much easier to read i.e.
>
> if (!list_empty)
> grab&remove first item;
> if (!list_empty)
> grab&remove 2nd item;
>
> Care to follow up with a patch for that?
>
> Thanks, Daniel
This needs to be kept as a loop because if there are two consecutive
requests for the same context they are squashed. Also the non-squashed
requests are not removed here (unfortunately the remove is in the next
patch).

>
> > + if (!req0)
> > + req0 = cursor;
> > + else if (req0->ctx == cursor->ctx) {
This:

> > + /* Same ctx: ignore first request, as second request
> > + * will update tail past first request's workload */
> > + list_del(&req0->execlist_link);
> > + i915_gem_context_unreference(req0->ctx);
> > + kfree(req0);
> > + req0 = cursor;
> > + } else {
> > + req1 = cursor;
> > + break;
> > + }
> > + }
> > +
> > + BUG_ON(execlists_submit_context(ring, req0->ctx, req0->tail,
> > + req1? req1->ctx : NULL, req1? req1->tail : 0)); }
> > +
> > +static int execlists_context_queue(struct intel_engine_cs *ring,
> > + struct intel_context *to,
> > + u32 tail)
> > +{
> > + struct intel_ctx_submit_request *req = NULL;
> > + unsigned long flags;
> > + bool was_empty;
> > +
> > + req = kzalloc(sizeof(*req), GFP_KERNEL);
> > + if (req == NULL)
> > + return -ENOMEM;
> > + req->ctx = to;
> > + i915_gem_context_reference(req->ctx);
> > + req->ring = ring;
> > + req->tail = tail;
> > +
> > + spin_lock_irqsave(&ring->execlist_lock, flags);
> > +
> > + was_empty = list_empty(&ring->execlist_queue);
> > + list_add_tail(&req->execlist_link, &ring->execlist_queue);
> > + if (was_empty)
> > + execlists_context_unqueue(ring);
> > +
> > + spin_unlock_irqrestore(&ring->execlist_lock, flags);
> > +
> > + return 0;
> > +}
> > +
> > static int logical_ring_invalidate_all_caches(struct intel_ringbuffer
> > *ringbuf) {
> > struct intel_engine_cs *ring = ringbuf->ring; @@ -405,8 +462,7 @@
> > void intel_logical_ring_advance_and_submit(struct intel_ringbuffer
> *ringbuf)
> > if (intel_ring_stopped(ring))
> > return;
> >
> > - /* FIXME: too cheeky, we don't even check if the ELSP is ready */
> > - execlists_submit_context(ring, ctx, ringbuf->tail, NULL, 0);
> > + execlists_context_queue(ring, ctx, ringbuf->tail);
> > }
> >
> > static int logical_ring_alloc_seqno(struct intel_engine_cs *ring, @@
> > -850,6 +906,9 @@ static int logical_ring_init(struct drm_device *dev, struct
> intel_engine_cs *rin
> > INIT_LIST_HEAD(&ring->request_list);
> > init_waitqueue_head(&ring->irq_queue);
> >
> > + INIT_LIST_HEAD(&ring->execlist_queue);
> > + spin_lock_init(&ring->execlist_lock);
> > +
> > ret = intel_lr_context_deferred_create(dctx, ring);
> > if (ret)
> > return ret;
> > diff --git a/drivers/gpu/drm/i915/intel_lrc.h
> > b/drivers/gpu/drm/i915/intel_lrc.h
> > index b59965b..14492a9 100644
> > --- a/drivers/gpu/drm/i915/intel_lrc.h
> > +++ b/drivers/gpu/drm/i915/intel_lrc.h
> > @@ -60,4 +60,12 @@ int intel_execlists_submission(struct drm_device
> *dev, struct drm_file *file,
> > u64 exec_start, u32 flags);
> > u32 intel_execlists_ctx_id(struct drm_i915_gem_object *ctx_obj);
> >
> > +struct intel_ctx_submit_request {
> > + struct intel_context *ctx;
> > + struct intel_engine_cs *ring;
> > + u32 tail;
> > +
> > + struct list_head execlist_link;
> > +};
> > +
> > #endif /* _INTEL_LRC_H_ */
> > diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h
> > b/drivers/gpu/drm/i915/intel_ringbuffer.h
> > index c885d5c..6358823 100644
> > --- a/drivers/gpu/drm/i915/intel_ringbuffer.h
> > +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
> > @@ -223,6 +223,8 @@ struct intel_engine_cs {
> > } semaphore;
> >
> > /* Execlists */
> > + spinlock_t execlist_lock;
> > + struct list_head execlist_queue;
> > u32 irq_keep_mask; /* bitmask for interrupts that should not
> be masked */
> > int (*emit_request)(struct intel_ringbuffer *ringbuf);
> > int (*emit_flush)(struct intel_ringbuffer *ringbuf,
> > --
> > 1.7.9.5
> >
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx@lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch