On Thu, May 19, 2016 at 04:44:03PM +0100, Tvrtko Ursulin wrote:
>
> On 19/05/16 12:32, Chris Wilson wrote:
> >Avoid the two calls to ktime_get_raw_ns() (at best it reads the TSC) as
> >we only need to compute the elapsed time for a timed wait.
> >
> >v2: Eliminate the unused local variable reducing the function size by 64
> >bytes (using the storage space on the callers stack rather than adding
> >to our stack frame)
> >
> >Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> >---
> > drivers/gpu/drm/i915/i915_gem.c | 14 +++++---------
> > 1 file changed, 5 insertions(+), 9 deletions(-)
> >
> >diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> >index b48a3b46e86f..2c254cf49c15 100644
> >--- a/drivers/gpu/drm/i915/i915_gem.c
> >+++ b/drivers/gpu/drm/i915/i915_gem.c
> >@@ -1215,7 +1215,6 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
> > int state = interruptible ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE;
> > struct intel_wait wait;
> > unsigned long timeout_remain;
> >- s64 before = 0; /* Only to silence a compiler warning. */
> > int ret = 0;
> >
> > might_sleep();
> >@@ -1234,12 +1233,9 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
> > if (*timeout == 0)
> > return -ETIME;
> >
> >+ /* Record current time in case interrupted, or wedged */
> > timeout_remain = nsecs_to_jiffies_timeout(*timeout);
> >-
> >- /*
> >- * Record current time in case interrupted by signal, or wedged.
> >- */
> >- before = ktime_get_raw_ns();
> >+ *timeout += ktime_get_raw_ns();
> > }
> >
> > trace_i915_gem_request_wait_begin(req);
> >@@ -1296,9 +1292,9 @@ complete:
> > trace_i915_gem_request_wait_end(req);
> >
> > if (timeout) {
> >- s64 tres = *timeout - (ktime_get_raw_ns() - before);
> >-
> >- *timeout = tres < 0 ? 0 : tres;
> >+ *timeout -= ktime_get_raw_ns();
> >+ if (*timeout < 0)
> >+ *timeout = 0;
> >
> > /*
> > * Apparently ktime isn't accurate enough and occasionally has a
> >
>
> I think this is bad, better have a local than play games with
> callers storage.
It's smaller faster code :-)
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
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