On Fri, Feb 2, 2018 at 7:18 PM, Andy Lutomirski <l...@kernel.org> wrote:
> On Fri, Feb 2, 2018 at 1:24 AM, Andy Lutomirski <l...@kernel.org> wrote:
>> On Thu, Feb 1, 2018 at 9:20 PM, Chris Wilson <ch...@chris-wilson.co.uk> 
>> wrote:
>>> Quoting Andy Lutomirski (2018-02-01 21:04:30)
>>>> I got this after a recent suspend/resume:
>>>>
>>>> Feb 01 09:44:34 laptop systemd-logind[2412]: Lid closed.
>>>> Feb 01 09:44:34 laptop systemd-logind[2412]: device-enumerator: scan all 
>>>> dirs
>>>> Feb 01 09:44:34 laptop systemd-logind[2412]:   device-enumerator:
>>>> scanning /sys/bus
>>>> Feb 01 09:44:34 laptop systemd-logind[2412]:   device-enumerator:
>>>> scanning /sys/class
>>>> Feb 01 09:44:34 laptop systemd-logind[2412]: Failed to open
>>>> configuration file '/etc/systemd/sleep.conf': No such file or
>>>> directory
>>>> Feb 01 09:44:34 laptop systemd-logind[2412]: Suspending...
>>>> Feb 01 09:44:34 laptop systemd-logind[2412]: Sent message type=signal
>>>> sender=n/a destination=n/a object=/org/freedesktop/login1
>>>> interface=org.freedesktop.login1.Manager member=PrepareForSleep
>>>> cookie=570 reply
>>>> Feb 01 09:44:34 laptop systemd-logind[2412]: Got message
>>>> type=method_call sender=:1.46 destination=:1.1
>>>> object=/org/freedesktop/login1/session/_32
>>>> interface=org.freedesktop.login1.Session member=ReleaseDevice
>>>> Feb 01 09:44:34 laptop systemd-logind[2412]: Sent message type=signal
>>>> sender=n/a destination=:1.46
>>>> object=/org/freedesktop/login1/session/_32
>>>> interface=org.freedesktop.login1.Session member=PauseDevice cookie
>>>> Feb 01 09:44:34 laptop gnome-shell[2630]: Failed to apply DRM plane
>>>> transform 0: Permission denied
>>>> Feb 01 09:44:34 laptop gnome-shell[2630]: drmModeSetCursor2 failed
>>>> with (Permission denied), drawing cursor with OpenGL from now on
>>>>
>>>> But I don't see the word "cursor" in my system logs before the first
>>>> suspend.  What am I looking for?  This is Fedora 27 running a Gnome
>>>> Wayland session, but it hasn't been reinstalled in some time, so it's
>>>> possible that there are some weird settings sitting around.  But I did
>>>> check and I have no weird i915 parameters.
>>>
>>> You are using gnome-shell as the display server. From that it appears to
>>> have started off with a HW cursor and switched to a SW cursor after
>>> suspend. Did you notice a change in behaviour? After rebooting or just
>>> restarting gnome-shell?
>>
>> I think it's less consistently bad after a reboot before suspending.
>>
>>>
>>>> Also, are these things potentially related:
>>>>
>>>> [ 3067.702527] [drm:intel_pipe_update_start [i915]] *ERROR* Potential
>>>> atomic update failure on pipe A
>>>
>>> They are just "missed the immediate vblank for the screen update"
>>> messages. Should not be related to PSR, but may cause jitter by delaying
>>> the odd screen update.
>>
>> I just got this one, and the timestamp is at least reasonably close to
>> a giant latency spike:
>>
>> [  288.799654] [drm:intel_pipe_update_end [i915]] *ERROR* Atomic
>> update failure on pipe A (start=31 end=32) time 15 us, min 1073, max
>> 1079, scanline start 1087, end 1088
>>
>>>
>>>> As I'm typing this, I've seen a couple instances of what seems like a
>>>> full *second* of cursor latency, but I've only gotten the potential
>>>> atomic update failure once.
>>>>
>>>> And is there any straightforward tracing to do to distinguish between
>>>> PSR exit latency and other potential sources of latency?
>>>
>>> It looks plausible that we could at least report how long it takes the
>>> registers to reflect the change in state (but we don't). The best source
>>> of information atm is /sys/kernel/debug/dri/0/i915_edp_psr_status.
>>
>> Hmm.
>>
>> I went and looked at the code, and I noticed what could be bugs or
>> could (more likely) be my confusion since I don't know this code at
>> all:
>>
>> intel_single_frame_update() does something inscrutable to me, but I
>> imagine it does something that causes the next page flip to get
>> noticed by the panel even with PSR on.  But how does the code that
>> calls it know that anything happened?  (Looking at the commit history,
>> maybe this is something special that's only needed on some platforms
>> but doesn't replace the normal PSR exit sequence.)
>>
>> Perhaps more interestingly, intel_psr_flush() does this:
>>
>>     /* By definition flush = invalidate + flush */
>>     if (frontbuffer_bits)
>>         intel_psr_exit(dev_priv);
>>
>>     if (!dev_priv->psr.active && !dev_priv->psr.busy_frontbuffer_bits)
>>         if (!work_busy(&dev_priv->psr.work.work))
>>             schedule_delayed_work(&dev_priv->psr.work,
>>                           msecs_to_jiffies(100));
>>
>> I'm guessing that the idea is that we're turning off PSR because we
>> want the panel to update and we expect that, in 100ms, the update will
>> have hit the panel and we'll have been idle long enough for it to make
>> sense to re-enter PSR.  IOW, the code wants PSR to be off for at least
>> 100ms and then to turn back on.  But this code actually says "turn PSR
>> back on in at *most* 100ms".  What happens if there are two screen
>> updates 99ms apart?  The first one should work fine, but the next one
>> will hit with 1ms left on the delayed work, and intel_psr_work() will
>> get called in 1ms.  There's some magic with busy_frontbuffer_bits, but
>> it seems questionable to me that intel_psr_flush() clears
>> busy_frontbuffer_bits and *then* calls intel_psr_exit().
>>
>> Naively, I would expect that PSR needs to be kept off until the vblank
>> following the page flip.
>>
>> Also, in intel_psr_work(), shouldn't this code:
>>
>>     /*
>>      * The delayed work can race with an invalidate hence we need to
>>      * recheck. Since psr_flush first clears this and then reschedules we
>>      * won't ever miss a flush when bailing out here.
>>      */
>>     if (dev_priv->psr.busy_frontbuffer_bits)
>>         goto unlock;
>>
>> re-arm the delayed work?
>>
>> Anyway, this is all on a 4.14 kernel.  I should update to 4.16 and see
>> what happens.
>
> I updated to 4.15, and the situation is much worse.  With
> enable_psr=1, the system survives for several seconds and then the
> screen stops updating entirely.  If I boot with i915.enable_psr=1, I
> get to the Fedora login screen and then the system dies.  If I set
> enable_psr=1 using sysfs, it does a bit after the next resume.  It
> seems like it also sometimes hangs even worse a bit after the screen
> stops updating, but it's hard to tell.
>
> I see this in my logs:
>
> [drm:drm_atomic_helper_wait_for_flip_done [drm_kms_helper]] *ERROR*
> [CRTC:37:pipe A] flip_done timed out
>
> Sometimes I see this a bit later:
>
> [drm:drm_atomic_helper_wait_for_dependencies [drm_kms_helper]] *ERROR*
> [CRTC:37:pipe A] flip_done timed out

I filed:

https://bugs.freedesktop.org/show_bug.cgi?id=104918
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