2016-07-12 19:21 GMT+01:00 Matt Roper <matthew.d.roper at intel.com>:
> On Tue, Jul 12, 2016 at 01:36:03PM -0400, Lyude wrote: > > Since the watermark calculations for Skylake are still broken, we're apt > > to hitting underruns very easily under multi-monitor configurations. > > While it would be lovely if this was fixed, it's not. Another problem > > that's been coming from this however, is the mysterious issue of > > underruns causing full system hangs. An easy way to reproduce this with > > a skylake system: > > > > - Get a laptop with a skylake GPU, and hook up two external monitors to > > it > > - Move the cursor from the built-in LCD to one of the external displays > > as quickly as you can > > - You'll get a few pipe underruns, and eventually the entire system will > > just freeze. > > > > After doing a lot of investigation and reading through the bspec, I > > found the existence of the SAGV, which is responsible for adjusting the > > system agent voltage and clock frequencies depending on how much power > > we need. According to the bspec: > > > > "The display engine access to system memory is blocked during the > > adjustment time. SAGV defaults to enabled. Software must use the > > GT-driver pcode mailbox to disable SAGV when the display engine is not > > able to tolerate the blocking time." > > > > The rest of the bspec goes on to explain that software can simply leave > > the SAGV enabled, and disable it when we use interlaced pipes/have more > > then one pipe active. > > > > Sure enough, with this patchset the system hangs resulting from pipe > > underruns on Skylake have completely vanished on my T460s. Additionally, > > the bspec mentions turning off the SAGV with more then one pipe > enabled > > as a workaround for display underruns. While this patch doesn't entirely > > fix that, it looks like it does improve the situation a little bit so > > it's likely this is going to be required to make watermarks on Skylake > > fully functional. > > > > Changes since v2: > > - Really apply minor style nitpicks to patch this time > > Changes since v1: > > - Added comments about this probably being one of the requirements to > > fixing Skylake's watermark issues > > - Minor style nitpicks from Matt Roper > > - Disable these functions on Broxton, since it doesn't have an SAGV > > > > Cc: Matt Roper <matthew.d.roper at intel.com> > > Cc: Daniel Vetter <daniel.vetter at ffwll.ch> > > Cc: Ville Syrjälä <ville.syrjala at linux.intel.com> > > Signed-off-by: Lyude <cpaul at redhat.com> > > I don't have a SKL to try this out on (only BXT here), but this matches > my interpretation of the current bspec text, so > > Reviewed-by: Matt Roper <matthew.d.roper at intel.com> > > I think this also applies to > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94625 > > Yes, this does sound very similar to the problems I were having in that report. Vacation etc. so haven't found time to try the 4.6 kernel yet, and now I will be travelling until next week. If someone is easily able to prepare a kernel for Fedora 24 with this patch it's more likely I can find time to try it next week (on Dell XPS 9550 with 1 or 2 external monitors). I should mention that there was a brief period in 4.4.4-4.4.9 or so that seemed to work fairly stable compared to both 4.3 and 4.5. /Oskar -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://lists.freedesktop.org/archives/dri-devel/attachments/20160713/e7fd996f/attachment-0001.html>
