From: Daniel Vetter <daniel@ffwll.ch>
To: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
Chi Ding <chix.ding@intel.com>
Subject: Re: [PATCH] drm/i915: Force vblanks around evasion when i915.watermark_test is set.
Date: Tue, 14 Jun 2016 17:48:46 +0200 [thread overview]
Message-ID: <20160614154846.GT1338@phenom.ffwll.local> (raw)
In-Reply-To: <473c83c2-8bcb-2acf-b0dc-71e50fcd00dc@linux.intel.com>
On Tue, Jun 14, 2016 at 08:27:57AM +0200, Maarten Lankhorst wrote:
> Op 13-06-16 om 16:45 schreef Daniel Vetter:
> > On Thu, Jun 09, 2016 at 01:36:50PM +0200, Maarten Lankhorst wrote:
> >> This will make it more likely that intermediary watermarks cause fifo
> >> underruns, which is useful when writing watermark specific tests,
> >> to make it more likely to trigger FIFO underruns in intermediary watermarks.
> > That's surprising ... with the vblank_wait added you're pretty much
> > guaranteed to never hit the evasion case. Note that the vblank evasion
> > code also just does a vblank wait if it detects a possible collision.
> >
> > Given that I'd have assumed that this simply slows down atomic flips,
> > which is probably not what we want for testing all. Does this really help?
> > Any ideas why?
> This is a sanity check on the intermediate watermarks. The vblank test will ensure
> that the old plane configuration doesn't cause underruns with watermarks, and that
> the intermediate watermarks will work correctly with the new plane configuration too.
>
> I think the latter vblank_wait may be killed, but the former could be really useful,
> for example to find correct watervblank values in CHV.
Why can't we do the vblank wait in userspace? If we wait 1 vblank (or just
for the drm event of the previous commit), and then immediately issue the
next one, we will also run with intermediate watermarks for a full frame.
At least I still don't see a super-short race window for which we need to
have code in the kernel to properly provoke it ...
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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prev parent reply other threads:[~2016-06-14 15:48 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-09 11:36 [PATCH] drm/i915: Force vblanks around evasion when i915.watermark_test is set Maarten Lankhorst
2016-06-13 14:45 ` Daniel Vetter
2016-06-14 6:27 ` Maarten Lankhorst
2016-06-14 15:48 ` Daniel Vetter [this message]
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