Re: [PATCH 1/2] drm/i915: Break busywaiting for requests on pending signals

Hi,

On 15/11/15 13:32, Chris Wilson wrote:

The busywait in __i915_spin_request() does not respect pending signals and so may consume the entire timeslice for the task instead of returning to userspace to handle the signal.

Obviously correct to break the spin, but if spending a jiffie to react to signals was the only problem then it is not too severe.

Add something to the commit message about how it was found/reported and about the severity of impact, etc?

Otherwise,

Reviewed-by: Tvrtko Ursulin tvrtko.ursulin@intel.com

Fixes regression from commit 2def4ad99befa25775dd2f714fdd4d92faec6e34 [v4.2] Author: Chris Wilson chris@chris-wilson.co.uk Date: Tue Apr 7 16:20:41 2015 +0100

  drm/i915: Optimistically spin for the request completion

Signed-off-by: Chris Wilson chris@chris-wilson.co.uk Cc: Jens Axboe axboe@kernel.dk Cc; "Rogozhkin, Dmitry V" dmitry.v.rogozhkin@intel.com Cc: Daniel Vetter daniel.vetter@ffwll.ch Cc: Tvrtko Ursulin tvrtko.ursulin@linux.intel.com Cc: Eero Tamminen eero.t.tamminen@intel.com Cc: "Rantala, Valtteri" valtteri.rantala@intel.com Cc: stable@kernel.vger.org

---

drivers/gpu/drm/i915/i915_gem.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c index 5cf4a1998273..740530c571d1 100644 --- a/drivers/gpu/drm/i915/i915_gem.c +++ b/drivers/gpu/drm/i915/i915_gem.c @@ -1146,7 +1146,7 @@ static bool missed_irq(struct drm_i915_private *dev_priv, return test_bit(ring->id, &dev_priv->gpu_error.missed_irq_rings); }

-static int __i915_spin_request(struct drm_i915_gem_request *req) +static int __i915_spin_request(struct drm_i915_gem_request *req, int state) { unsigned long timeout;

@@ -1158,6 +1158,9 @@ static int __i915_spin_request(struct drm_i915_gem_request *req) if (i915_gem_request_completed(req, true)) return 0;

• if (signal_pending_state(state, current))
  

• 	break;
  

• if (time_after_eq(jiffies, timeout)) break;

@@ -1197,6 +1200,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req, struct drm_i915_private *dev_priv = dev->dev_private; const bool irq_test_in_progress = ACCESS_ONCE(dev_priv->gpu_error.test_irq_rings) & intel_ring_flag(ring);

• int state = interruptible ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE; DEFINE_WAIT(wait); unsigned long timeout_expire; s64 before, now;

@@ -1221,7 +1225,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req, before = ktime_get_raw_ns();

/* Optimistic spin for the next jiffie before touching IRQs */

• ret = __i915_spin_request(req);

• ret = __i915_spin_request(req, state); if (ret == 0) goto out;

@@ -1233,8 +1237,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req, for (;;) { struct timer_list timer;

• prepare_to_wait(&ring->irq_queue, &wait,
  

• 		interruptible ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE);
  

• prepare_to_wait(&ring->irq_queue, &wait, state);
  
  

  /* We need to check whether any gpu reset happened in between

  • the caller grabbing the seqno and now ... */

@@ -1252,7 +1255,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req, break; }

• if (interruptible && signal_pending(current)) {
  

• if (signal_pending_state(state, current)) {
  ret = -ERESTARTSYS;
  break;
  

  }