Re: [PATCH v2 11/28] drm/i915: Add IRQ friendly request deference facility

Daniel, Thomas
2014-11-18T09:34:48Z

> -----Original Message-----
> From: Intel-gfx [mailto:intel-gfx-bounces@lists.freedesktop.org] On Behalf
> Of John.C.Harrison@Intel.com
> Sent: Friday, November 14, 2014 12:19 PM
> To: Intel-GFX@Lists.FreeDesktop.Org
> Subject: [Intel-gfx] [PATCH v2 11/28] drm/i915: Add IRQ friendly request
> deference facility
>
> From: John Harrison <John.C.Harrison@Intel.com>
>
> The next patches in the series convert some display related seqno usage to
> request structure usage. However, the request dereference introduced
> must be done from interrupt context. As the dereference potentially
> involves freeing the request structure and thus calling lots of non-interrupt
> friendly code, this poses a problem.
>
> The solution is to add an IRQ friendly version of the dereference function. All
> this does is to add the request structure to a 'delayed free' list and return.
> The retire code, which is run periodically, then processes this list and does
> the actual dereferencing of the request structures.
>
> v2: Added a count to allow for multiple IRQ dereferences of the same
> request at a time.
>
> For: VIZ-4377
> Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
> ---
> drivers/gpu/drm/i915/i915_drv.h | 7 +++++++
> drivers/gpu/drm/i915/i915_gem.c | 33
> +++++++++++++++++++++++++++++++
> drivers/gpu/drm/i915/intel_lrc.c | 2 ++
> drivers/gpu/drm/i915/intel_ringbuffer.c | 3 +++
> drivers/gpu/drm/i915/intel_ringbuffer.h | 2 ++
> 5 files changed, 47 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.h
> b/drivers/gpu/drm/i915/i915_drv.h index 180b674..87cb355 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2019,6 +2019,10 @@ struct drm_i915_gem_request {
> struct drm_i915_file_private *file_priv;
> /** file_priv list entry for this request */
> struct list_head client_list;
> +
> + /** deferred free list for dereferencing from IRQ context */
> + struct list_head delay_free_list;
> + uint32_t delay_free_count;
> };
>
> void i915_gem_request_free(struct kref *req_ref); @@ -2044,9 +2048,12
> @@ i915_gem_request_reference(struct drm_i915_gem_request *req)
> static inline void i915_gem_request_unreference(struct
> drm_i915_gem_request *req) {
> + WARN_ON(!mutex_is_locked(&req->ring->dev->struct_mutex));
> kref_put(&req->ref, i915_gem_request_free); }
>
> +void i915_gem_request_unreference_irq(struct drm_i915_gem_request
> +*req);
> +
> static inline void i915_gem_request_assign(struct drm_i915_gem_request
> **pdst,
> struct drm_i915_gem_request *src)
> { diff --git a/drivers/gpu/drm/i915/i915_gem.c
> b/drivers/gpu/drm/i915/i915_gem.c index 60e5eec..8453bbd 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -2722,6 +2722,19 @@ void i915_gem_reset(struct drm_device *dev)
> i915_gem_restore_fences(dev);
> }
>
> +void i915_gem_request_unreference_irq(struct drm_i915_gem_request
> *req)
> +{
> + struct intel_engine_cs *ring = req->ring;
> + unsigned long flags;
> +
> + /* Need to add the req to a deferred dereference list to be
> processed
> + * outside of interrupt time */
> + spin_lock_irqsave(&ring->reqlist_lock, flags);
> + if (req->delay_free_count++ == 0)
> + list_add_tail(&req->delay_free_list, &ring-
> >delayed_free_list);
> + spin_unlock_irqrestore(&ring->reqlist_lock, flags); }
> +
> /**
> * This function clears the request list as sequence numbers are passed.
> */
> @@ -2796,6 +2809,25 @@ i915_gem_retire_requests_ring(struct
> intel_engine_cs *ring)
> ring->trace_irq_seqno = 0;
> }
>
> + while (!list_empty(&ring->delayed_free_list)) {
> + struct drm_i915_gem_request *request;
> + unsigned long flags;
> + uint32_t count;
> +
> + request = list_first_entry(&ring->delayed_free_list,
> + struct drm_i915_gem_request,
> + delay_free_list);
> +
> + spin_lock_irqsave(&request->ring->reqlist_lock, flags);
> + list_del(&request->delay_free_list);
> + count = request->delay_free_count;
> + request->delay_free_count = 0;
> + spin_unlock_irqrestore(&request->ring->reqlist_lock, flags);
> +
> + while (count-- > 0)
> + i915_gem_request_unreference(request);
> + }
> +
> WARN_ON(i915_verify_lists(ring->dev));
> }
>
> @@ -5055,6 +5087,7 @@ init_ring_lists(struct intel_engine_cs *ring) {
> INIT_LIST_HEAD(&ring->active_list);
> INIT_LIST_HEAD(&ring->request_list);
> + INIT_LIST_HEAD(&ring->delayed_free_list);

Same comment as before - multiple init points for this list.

Thomas.

> }
>
> void i915_init_vm(struct drm_i915_private *dev_priv, diff --git
> a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index eba0acd..db8efaa 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -1287,7 +1287,9 @@ static int logical_ring_init(struct drm_device *dev,
> struct intel_engine_cs *rin
> ring->dev = dev;
> INIT_LIST_HEAD(&ring->active_list);
> INIT_LIST_HEAD(&ring->request_list);
> + spin_lock_init(&ring->reqlist_lock);
> init_waitqueue_head(&ring->irq_queue);
> + INIT_LIST_HEAD(&ring->delayed_free_list);
>
> INIT_LIST_HEAD(&ring->execlist_queue);
> spin_lock_init(&ring->execlist_lock);
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c
> b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index 74c48ed..4338132 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -1808,6 +1808,8 @@ static int intel_init_ring_buffer(struct drm_device
> *dev,
> ring->dev = dev;
> INIT_LIST_HEAD(&ring->active_list);
> INIT_LIST_HEAD(&ring->request_list);
> + spin_lock_init(&ring->reqlist_lock);
> + INIT_LIST_HEAD(&ring->delayed_free_list);
> INIT_LIST_HEAD(&ring->execlist_queue);
> ringbuf->size = 32 * PAGE_SIZE;
> ringbuf->ring = ring;
> @@ -2510,6 +2512,7 @@ int intel_render_ring_init_dri(struct drm_device
> *dev, u64 start, u32 size)
> ring->dev = dev;
> INIT_LIST_HEAD(&ring->active_list);
> INIT_LIST_HEAD(&ring->request_list);
> + INIT_LIST_HEAD(&ring->delayed_free_list);
>
> ringbuf->size = size;
> ringbuf->effective_size = ringbuf->size; diff --git
> a/drivers/gpu/drm/i915/intel_ringbuffer.h
> b/drivers/gpu/drm/i915/intel_ringbuffer.h
> index 824f5884..3af7b7c 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.h
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
> @@ -262,6 +262,8 @@ struct intel_engine_cs {
> * outstanding.
> */
> struct list_head request_list;
> + spinlock_t reqlist_lock;
> + struct list_head delayed_free_list;
>
> /**
> * Do we have some not yet emitted requests outstanding?
> --
> 1.7.9.5
>
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