On Fri, 26 Oct 2018 16:26:03 +0200 Daniel Vetter <dan...@ffwll.ch> wrote:
> On Fri, Oct 26, 2018 at 3:57 PM Boris Brezillon > <boris.brezil...@bootlin.com> wrote: > > > > On Fri, 26 Oct 2018 15:30:26 +0200 > > Daniel Vetter <dan...@ffwll.ch> wrote: > > > > > On Thu, Oct 25, 2018 at 11:41:14AM +0200, Boris Brezillon wrote: > > > > On Thu, 25 Oct 2018 11:33:14 +0200 > > > > Daniel Vetter <dan...@ffwll.ch> wrote: > > > > > > > > > On Thu, Oct 25, 2018 at 10:09:31AM +0200, Boris Brezillon wrote: > > > > > > On Tue, 23 Oct 2018 15:44:43 +0200 > > > > > > Daniel Vetter <dan...@ffwll.ch> 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 <dan...@ffwll.ch> 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.brezil...@bootlin.com> > > > > > > > > > > --- > > > > > > > > > > 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. > > > > > > > > > > Yeah probably good enough. For our CI all we care about is the > > > > > warn/error > > > > > level dmesg output. Anything at that level is considered a CI > > > > > failure. > > > > > > > > So igt is grepping dmesg to detect when an underrun happens? > > > > > > No, but the CI runner is also observing dmesg. Anything in there at > > > warning or higher level is considered a failure. > > > > Eric, do you do the same when you launch the IGT testsuite? > > > > > > > > > > What do you need the debugfs file for? > > > > > > > > I just thought having a debugfs file to expose the underrun information > > > > would be cleaner than having to grep in dmesg to detect such failures. > > > > > > The issue is that you want to detect underruns everywhere, not just in the > > > specific tests you're checking for it. Anything that does a modeset could > > > cause an underrun (at least we've managed to do so pretty much everywhere > > > on i915 hw, if you misprogram is sufficiently). > > > > In my specific case, I want to have the IGT test check the underrun > > value while the test is being executed so that I know which exact > > configuration triggers the underrun situation. At least that's how I > > did to adjust/debug the HVS load tracking code. Maybe it's not really a > > problem when all we do is tracking regressions. > > Ok, that makes sense, and explains why you want the overall underrun > counter exposed in debugfs. Just one tiny detail which is not exactly related to this discussion but I thought I'd mention it here: underrun is actually not a counter, it's just a boolean. I used an atomic_t type to avoid having to add a spinlock to protect the variable (the variable is modified from an interrupt context and read from a non-atomic context). So, the acceptable values for underrun are currently 0 or 1. I can make it a counter if required. _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
