On Tue, 23 Oct 2018 15:44:43 +0200 Daniel Vetter <daniel@xxxxxxxx> wrote: > On Tue, Oct 23, 2018 at 09:55:08AM +0200, Boris Brezillon wrote: > > Hi Daniel, > > > > On Tue, 16 Oct 2018 14:57:43 +0200 > > Daniel Vetter <daniel@xxxxxxxx> wrote: > > > > > On Tue, Oct 16, 2018 at 11:40:45AM +0200, Boris Brezillon wrote: > > > > The HVS block is supposed to fill the pixelvalve FIFOs fast enough to > > > > meet the requested framerate. The problem is, the HVS and memory bus > > > > bandwidths are limited, and if we don't take these limitations into > > > > account we might end up with HVS underflow errors. > > > > > > > > This patch is trying to model the per-plane HVS and memory bus bandwidth > > > > consumption and take a decision at atomic_check() time whether the > > > > estimated load will fit in the HVS and membus budget. > > > > > > > > Note that we take an extra margin on the memory bus consumption to let > > > > the system run smoothly when other blocks are doing heavy use of the > > > > memory bus. Same goes for the HVS limit, except the margin is smaller in > > > > this case, since the HVS is not used by external components. > > > > > > > > Signed-off-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxx> > > > > --- > > > > This logic has been validated using a simple shell script and > > > > some instrumentation in the VC4 driver: > > > > > > > > - capture underflow errors at the HVS level and expose a debugfs file > > > > reporting those errors > > > > - add debugfs files to expose when atomic_check fails because of the > > > > HVS or membus load limitation or when it fails for other reasons > > > > > > > > The branch containing those modification is available here [1], and the > > > > script (which is internally using modetest) is here [2] (please note > > > > that I'm bad at writing shell scripts :-)). > > > > > > > > Note that those modification tend to over-estimate the load, and thus > > > > reject setups that might have previously worked, so we might want to > > > > adjust the limits to avoid that. > > > > > > > > [1]https://github.com/bbrezillon/linux/tree/vc4/hvs-bandwidth-eval > > > > [2]https://github.com/bbrezillon/vc4-hvs-bandwidth-test > > > > > > Any interest in using igt to test this stuff? We have at least a bunch of > > > tests already in there that try all kinds of plane setups. And we use > > > those to hunt for underruns on i915 hw. > > > > > > Wrt underrun reporting: On i915 we just dump them into dmesg at the error > > > level, using DRM_ERROR, > > > > Are you masking the underrun interrupt after it's been reported? If we > > don't do that on VC4 we just end up flooding the kernel-log buffer until > > someone comes and update the config. > > Yeah we do that too. Rule is that a full modeset will clear any underrun > masking (so tests need to make sure they start with a modeset, or it'll be > for nothing). > > > > > > plus a tracepoint. See e.g. > > > intel_pch_fifo_underrun_irq_handler(). If there's interest we could > > > perhaps extract this into something common, similar to what was done with > > > crc support already. > > > > > > > I'm not a big fan of hardcoded trace points in general (because of the > > whole "it's part of the stable ABI" thing), and in this case, making the > > tracepoint generic sounds even more risky to me. Indeed, how can we know > > about all the HW specific bits one might want to expose. For instance, > > I see the intel underrun tracepoint exposes a struct with a frame and > > scanline field, and AFAICT, we don't have such information in the VC4 > > case. > > > > Any opinion on that? > > It's only abi if you're unlucky. If it's just for debugging and > validation, you can change it again. Tbh, no idea why we even have these > tracepoints, they're fairly useless imo. CI only relies upon the dmesg > output. Maybe run git blame and ask the original author, we can probably > update them to suit our needs. Okay, I think I'll go for a generic debugfs entry that returns true when an underrun error happened since the last modeset, false otherwise. Next question is: should I attach the underrun status to the drm_device or have one per CRTC? In my case, I only care about the "has an underrun error occurred on any of the active CRTC" case, so I'd vote for a per-device underrun status. _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
