From: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
To: Daniel Vetter <daniel@ffwll.ch>, ville.syrjala@linux.intel.com
Cc: intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org
Subject: Re: [PATCH 11/11] drm: Fix vblank timestamp races
Date: Tue, 22 Sep 2015 13:15:01 +0200 [thread overview]
Message-ID: <56013835.4010706@linux.intel.com> (raw)
In-Reply-To: <20150922091050.GX3383@phenom.ffwll.local>
Op 22-09-15 om 11:10 schreef Daniel Vetter:
> On Mon, Sep 14, 2015 at 10:43:52PM +0300, ville.syrjala@linux.intel.com wrote:
>> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>>
>> The vblank timestamp ringbuffer only has two entries, so if the
>> vblank->count is incremented by an even number readers may end up seeing
>> the new vblank timestamp alongside the old vblank counter value.
>>
>> Fix the problem by storing the vblank counter in a ringbuffer as well,
>> and always increment the ringbuffer "slot" by one when storing a new
>> timestamp+counter pair.
>>
>> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Imo if we bother with this we might as well just switch over to using
> full-blown seqlocks. They internally use a two-stage update which means
> race-free even with just one copy of the data we protect. Also more
> standardized to boot.
>
> Series looks good otherwise, I'll wait for Maarten to r-b it and then pull
> it in.
>
R-b for 1-10.
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next prev parent reply other threads:[~2015-09-22 11:15 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-14 19:43 [PATCH 00/11] drm: vblank fixes and timestamp based missed vblank guesttimation ville.syrjala
2015-09-14 19:43 ` [PATCH 01/11] drm: s/int crtc/unsigned int pipe/ straggles ville.syrjala
2015-09-15 7:29 ` Thierry Reding
2015-09-22 9:05 ` Daniel Vetter
2015-09-14 19:43 ` [PATCH 02/11] drm: Move timestamping constants into drm_vblank_crtc ville.syrjala
2015-09-16 13:21 ` Maarten Lankhorst
2015-09-14 19:43 ` [PATCH 03/11] drm: Stop using linedur_ns and pixeldur_ns for vblank timestamps ville.syrjala
2015-09-14 19:43 ` [PATCH 04/11] drm: Kill pixeldur_ns ville.syrjala
2015-09-14 19:43 ` [PATCH 05/11] drm/i915: Fix vblank count variable types ville.syrjala
2015-09-14 19:43 ` [PATCH 06/11] drm: Pass flags to drm_update_vblank_count() ville.syrjala
2015-09-14 19:43 ` [PATCH 07/11] drm: Limit the number of .get_vblank_counter() retries ville.syrjala
2015-09-14 19:43 ` [PATCH 08/11] drm: Clean up drm_calc_vbltimestamp_from_scanoutpos() vbl_status ville.syrjala
2015-09-14 19:43 ` [PATCH 09/11] drm: store_vblank() is never called with NULL timestamp ville.syrjala
2015-09-14 19:43 ` [PATCH 10/11] drm: Use vblank timestamps to guesstimate how many vblanks were missed ville.syrjala
2015-09-28 2:57 ` Michel Dänzer
2015-09-30 14:42 ` Thierry Reding
2015-09-14 19:43 ` [PATCH 11/11] drm: Fix vblank timestamp races ville.syrjala
2015-09-22 9:10 ` Daniel Vetter
2015-09-22 11:15 ` Maarten Lankhorst [this message]
2015-09-22 11:31 ` Daniel Vetter
2015-09-22 12:36 ` Ville Syrjälä
2015-09-22 12:57 ` Daniel Vetter
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