[Intel-gfx] [PATCH 3/7] drm/i915: Spin opportunistically in wait_for

[Chris Wilson]

On Wed, May 18, 2016 at 10:20:22AM +0200, Daniel Vetter wrote:
> On Tue, May 17, 2016 at 06:43:24PM +0300, Mika Kuoppala wrote:
> > Usually the condition we are after appears within very short time.
> > Spin few times before going into sleep. With this approximately
> > half of the wait_for in init path will take the fast path without
> > sleeping.
> > 
> > Signed-off-by: Mika Kuoppala <mika.kuoppala at intel.com>
> 
> Some numbers on how much time this saved would be nice.
> 
> Reviewed-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> 
> > ---
> >  drivers/gpu/drm/i915/intel_drv.h | 14 ++++++++++----
> >  1 file changed, 10 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> > index 488141929a7a..c225605c727c 100644
> > --- a/drivers/gpu/drm/i915/intel_drv.h
> > +++ b/drivers/gpu/drm/i915/intel_drv.h
> > @@ -39,7 +39,7 @@
> >  #include <drm/drm_atomic.h>
> >  
> >  /**
> > - * _wait_for_ms - magic (register) wait macro
> > + * __wait_for_ms - magic (register) wait macro
> >   *
> >   * Does the right thing for modeset paths when run under kdgb or similar atomic
> >   * contexts. Note that it's important that we check the condition again after
> > @@ -50,17 +50,22 @@
> >   * drm_can_sleep() can be removed and in_atomic()/!in_atomic() asserts
> >   * added.
> >   */
> > -#define _wait_for_ms(COND, TIMEOUT_MS, SLEEP_US) ({ \
> > +#define __wait_for_ms(COND, TIMEOUT_MS, SLEEP_US, SPIN_COUNT) ({	\
> >  	const unsigned long timeout__ =					\
> >  		jiffies + msecs_to_jiffies(TIMEOUT_MS) + 1;		\
> > +	unsigned int c__ = 0;						\
> >  	int ret__ = 0;							\
> > +									\
> >  	while (!(COND)) {						\
> >  		if (time_after(jiffies, timeout__)) {			\
> >  			if (!(COND))					\
> >  				ret__ = -ETIMEDOUT;			\
> >  			break;						\
> >  		}							\
> > -		if ((SLEEP_US) && drm_can_sleep()) {			\
> > +									\
> > +		if (++c__ > (SPIN_COUNT) &&				\
> > +		    (SLEEP_US) &&					\

Could we kill SLEEP_US here in patch 0?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre