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From: Ben Widawsky <ben@bwidawsk.net>
To: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>, Intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH] drm/i915: Reduce locking in command submission
Date: Thu, 15 Jan 2015 15:42:42 -0800	[thread overview]
Message-ID: <20150115234242.GD24627@bwidawsk.net> (raw)
In-Reply-To: <54B7F35A.9050405@linux.intel.com>

On Thu, Jan 15, 2015 at 05:05:30PM +0000, Tvrtko Ursulin wrote:
> 
> On 01/15/2015 04:54 PM, Ben Widawsky wrote:
> >On Thu, Jan 15, 2015 at 11:21:30AM +0000, Tvrtko Ursulin wrote:
> >>From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> >>
> >>This eliminates six needless spin lock/unlock pairs when writing out ELSP. Apart
> >>from tidier code main benefit is between 0.51% and 0.73% speedup on some OGL
> >>tests under CHV (bench_OglBatch4 bench_OglDeferred respectively).
> >
> >With 95% confidence t-test on n=5
> >
> >>
> >>Kindly benchmarked by Ben Widawsky.
> >
> >FWIW, as I mentioned on IRC, I think the reduction of the unnecessary forcewake
> >(someone should fix the shadow register list) is probably more beneficial than
> >removing the spin on an uncontested lock. I was tempted to try that myself, but
> >I didn't have time or much interest since your patch accomplishes the same
> >thing.
> 
> I missed that IRC discussion, but I don't think it was doing forcewakes
> since the outer block in execlists_elsp_write bumps the counters which made
> I915_WRITE & co skip them.
> 
> Regards,
> 
> Tvrtko

I didn't check the locking but it looks like it could actually get decremented
once the spinlock is released. Probably never happens, but I think it's
possible.

I completely missed that block somehow. I think my eyes skipped over it because
how could getting forcewake take like 10+ lines :D
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  reply	other threads:[~2015-01-15 23:42 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-12-11 15:41 [RFC] drm/i915: Reduce locking in command submission Tvrtko Ursulin
2014-12-15 13:06 ` Daniel Vetter
2014-12-16 13:34   ` Tvrtko Ursulin
2015-01-14 10:13   ` Tvrtko Ursulin
2015-01-15 11:21 ` [PATCH] " Tvrtko Ursulin
2015-01-15 16:54   ` Ben Widawsky
2015-01-15 17:05     ` Tvrtko Ursulin
2015-01-15 23:42       ` Ben Widawsky [this message]
2015-01-16  0:19   ` shuang.he

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