Re: [PATCH 1/7] drm/i915: Mark context switch likely

[Ben Widawsky <ben@bwidawsk.net>]

On Fri, Apr 05, 2013 at 10:09:58AM +0300, Jani Nikula wrote:
> On Fri, 05 Apr 2013, Ben Widawsky <ben@bwidawsk.net> wrote:
> > Only the very first switch doesn't take the path.
> >
> > Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
> > ---
> >  drivers/gpu/drm/i915/i915_gem_context.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
> > index 94d873a..aa080ea 100644
> > --- a/drivers/gpu/drm/i915/i915_gem_context.c
> > +++ b/drivers/gpu/drm/i915/i915_gem_context.c
> > @@ -390,7 +390,7 @@ static int do_switch(struct i915_hw_context *to)
> >  	 * is a bit suboptimal because the retiring can occur simply after the
> >  	 * MI_SET_CONTEXT instead of when the next seqno has completed.
> >  	 */
> > -	if (from_obj != NULL) {
> > +	if (likely(from_obj)) {
> 
> Looking at the function, is this, uh, likely to make a difference?
> 

Probably not.

> Same goes for the unlikely in patches 4/7. (Yes, patch_es_ 4/7 - there's
> *two* patches 4/7 in the series! :o)

I don't see two, weird.

> 
> I'm just generally wary of adding (un)likely annotations. I don't think
> it matters that the annotation itself is obviously correct; IMHO the
> performance impact should matter.
> 
> </bikeshed>

Right. I actually stuck it in by accident, and decided to keep it only
because it serves as nice documentation. I suppose a comment would do
the same thing, but this also had a chance (albeit slight) to improve
things.

> 
> BR,
> Jani.
> 
> 
> >  		from_obj->base.read_domains = I915_GEM_DOMAIN_INSTRUCTION;
> >  		i915_gem_object_move_to_active(from_obj, ring);
> >  		/* As long as MI_SET_CONTEXT is serializing, ie. it flushes the
> > -- 
> > 1.8.2
> >
> > _______________________________________________
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> > Intel-gfx@lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Ben Widawsky, Intel Open Source Technology Center