Re: [PATCH 06/13] drm/i915: Only grab timestamps when needed

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Jan 08, 2016 at 11:29:45AM +0000, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> 
> No need to call ktime_get_raw_ns twice per unlimited wait and can
> also elimate a local variable.
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index de98dc41fb9f..c4f69579eb7a 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1246,7 +1246,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
>  	int state = interruptible ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE;
>  	DEFINE_WAIT(wait);
>  	unsigned long timeout_expire;
> -	s64 before, now;
> +	s64 before = 0;

Is gcc really this dense? Should be easy for it to spot that both branches
depend upon the same condition. Please remove that assignment. With that
changed:

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

>  	int ret;
>  
>  	WARN(!intel_irqs_enabled(dev_priv), "IRQs disabled");
> @@ -1266,14 +1266,17 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
>  			return -ETIME;
>  
>  		timeout_expire = jiffies + nsecs_to_jiffies_timeout(*timeout);
> +
> +		/*
> +		 * Record current time in case interrupted by signal, or wedged.
> +		 */
> +		before = ktime_get_raw_ns();
>  	}
>  
>  	if (INTEL_INFO(dev_priv)->gen >= 6)
>  		gen6_rps_boost(dev_priv, rps, req->emitted_jiffies);
>  
> -	/* Record current time in case interrupted by signal, or wedged */
>  	trace_i915_gem_request_wait_begin(req);
> -	before = ktime_get_raw_ns();
>  
>  	/* Optimistic spin for the next jiffie before touching IRQs */
>  	ret = __i915_spin_request(req, state);
> @@ -1331,11 +1334,10 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
>  	finish_wait(&ring->irq_queue, &wait);
>  
>  out:
> -	now = ktime_get_raw_ns();
>  	trace_i915_gem_request_wait_end(req);
>  
>  	if (timeout) {
> -		s64 tres = *timeout - (now - before);
> +		s64 tres = *timeout - (ktime_get_raw_ns() - before);
>  
>  		*timeout = tres < 0 ? 0 : tres;
>  
> -- 
> 1.9.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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