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'm able to get some debugging out before the system dies.  I see
intel_psr_flush() getting called a bunch, and I don't see
intel_psr_invalidate() being called at all.  I also see
intel_psr_work() activating psr as little as 2ms after
intel_psr_flush() finishes.  So I think the code is indeed buggy or at
least questionable.  I'd try to fix it (at least as well as I can
without knowing anything about how the PSR state machine actually
works), but the fact that the system hangs would make it very hard to
test.
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