[PATCH 6/6] drm/i915: Use irq work for coalescing-only dma-fence-work

[Thomas Hellström]

We are using a timeline-attached struct dma_fence_work to coalesce
dma-fences on eviction. In this mode we will not have a work callback
attached.
Similar to how the dma-fence-chain and dma-fence-array containers do this,
use irq work to signal to reduce latency.

Signed-off-by: Thomas Hellström <thomas.hellst...@linux.intel.com>
---
 drivers/gpu/drm/i915/i915_sw_fence_work.c | 36 ++++++++++++++++++-----
 drivers/gpu/drm/i915/i915_sw_fence_work.h |  2 ++
 2 files changed, 31 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_sw_fence_work.c 
b/drivers/gpu/drm/i915/i915_sw_fence_work.c
index 87cdb3158042..4573f537ada4 100644
--- a/drivers/gpu/drm/i915/i915_sw_fence_work.c
+++ b/drivers/gpu/drm/i915/i915_sw_fence_work.c
@@ -32,16 +32,17 @@ void dma_fence_work_timeline_attach(struct 
dma_fence_work_timeline *tl,
 {
        struct dma_fence *await;
 
+       might_sleep();
        if (tl->ops->get)
                tl->ops->get(tl);
 
-       spin_lock(&tl->lock);
+       spin_lock_irq(&tl->lock);
        await = tl->last_fence;
        tl->last_fence = dma_fence_get(&f->dma);
        f->dma.seqno = tl->seqno++;
        f->dma.context = tl->context;
        f->tl = tl;
-       spin_unlock(&tl->lock);
+       spin_unlock_irq(&tl->lock);
 
        if (await) {
                __i915_sw_fence_await_dma_fence(&f->chain, await, tl_cb);
@@ -53,13 +54,14 @@ static void dma_fence_work_timeline_detach(struct 
dma_fence_work *f)
 {
        struct dma_fence_work_timeline *tl = f->tl;
        bool put = false;
+       unsigned long irq_flags;
 
-       spin_lock(&tl->lock);
+       spin_lock_irqsave(&tl->lock, irq_flags);
        if (tl->last_fence == &f->dma) {
                put = true;
                tl->last_fence = NULL;
        }
-       spin_unlock(&tl->lock);
+       spin_unlock_irqrestore(&tl->lock, irq_flags);
        if (tl->ops->put)
                tl->ops->put(tl);
        if (put)
@@ -68,8 +70,6 @@ static void dma_fence_work_timeline_detach(struct 
dma_fence_work *f)
 
 static void dma_fence_work_complete(struct dma_fence_work *f)
 {
-       dma_fence_signal(&f->dma);
-
        if (f->ops->release)
                f->ops->release(f);
 
@@ -79,13 +79,32 @@ static void dma_fence_work_complete(struct dma_fence_work 
*f)
        dma_fence_put(&f->dma);
 }
 
+static void dma_fence_work_irq_work(struct irq_work *irq_work)
+{
+       struct dma_fence_work *f = container_of(irq_work, typeof(*f), irq_work);
+
+       dma_fence_signal(&f->dma);
+       if (f->ops->release)
+               /* Note we take the signaled path in dma_fence_work_work() */
+               queue_work(system_unbound_wq, &f->work);
+       else
+               dma_fence_work_complete(f);
+}
+
 static void dma_fence_work_work(struct work_struct *work)
 {
        struct dma_fence_work *f = container_of(work, typeof(*f), work);
 
+       if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &f->dma.flags)) {
+               dma_fence_work_complete(f);
+               return;
+       }
+
        if (f->ops->work)
                f->ops->work(f);
 
+       dma_fence_signal(&f->dma);
+
        dma_fence_work_complete(f);
 }
 
@@ -102,8 +121,10 @@ fence_notify(struct i915_sw_fence *fence, enum 
i915_sw_fence_notify state)
                dma_fence_get(&f->dma);
                if (test_bit(DMA_FENCE_WORK_IMM, &f->dma.flags))
                        dma_fence_work_work(&f->work);
-               else
+               else if (f->ops->work)
                        queue_work(system_unbound_wq, &f->work);
+               else
+                       irq_work_queue(&f->irq_work);
                break;
 
        case FENCE_FREE:
@@ -155,6 +176,7 @@ void dma_fence_work_init(struct dma_fence_work *f,
        dma_fence_init(&f->dma, &fence_ops, &f->lock, 0, 0);
        i915_sw_fence_init(&f->chain, fence_notify);
        INIT_WORK(&f->work, dma_fence_work_work);
+       init_irq_work(&f->irq_work, dma_fence_work_irq_work);
 }
 
 int dma_fence_work_chain(struct dma_fence_work *f, struct dma_fence *signal)
diff --git a/drivers/gpu/drm/i915/i915_sw_fence_work.h 
b/drivers/gpu/drm/i915/i915_sw_fence_work.h
index 6f41ee360133..c412bb4cb288 100644
--- a/drivers/gpu/drm/i915/i915_sw_fence_work.h
+++ b/drivers/gpu/drm/i915/i915_sw_fence_work.h
@@ -8,6 +8,7 @@
 #define I915_SW_FENCE_WORK_H
 
 #include <linux/dma-fence.h>
+#include <linux/irq_work.h>
 #include <linux/spinlock.h>
 #include <linux/workqueue.h>
 
@@ -77,6 +78,7 @@ struct dma_fence_work {
        struct i915_sw_dma_fence_cb cb;
 
        struct work_struct work;
+       struct irq_work irq_work;
 
        struct dma_fence_work_timeline *tl;
 
-- 
2.31.1