Op 30-01-17 om 09:17 schreef Daniel Vetter: > On Fri, Jan 27, 2017 at 03:08:45PM +0000, Chris Wilson wrote: >> On Fri, Jan 27, 2017 at 03:58:08PM +0100, Daniel Vetter wrote: >>> On Fri, Jan 27, 2017 at 02:31:55PM +0000, Chris Wilson wrote: >>>> On Fri, Jan 27, 2017 at 03:21:29PM +0100, Daniel Vetter wrote: >>>>> On Fri, Jan 27, 2017 at 09:30:50AM +0000, Chris Wilson wrote: >>>>>> On Thu, Jan 26, 2017 at 04:59:21PM +0100, Maarten Lankhorst wrote: >>>>>>> When writing some testcases for nonblocking modesets. I found out that the >>>>>>> infinite wait on the old fb was causing issues. >>>>>> The crux of the issue here is the locked wait for old dependencies and >>>>>> the inability to inject the intel_prepare_reset disabling of all planes. >>>>>> There are a couple of locked waits on struct_mutex within the modeset >>>>>> locks for intel_overlay and if we happen to be using the display plane >>>>>> for the first time. >>>>>> >>>>>> The first I suggested solving using fences to track dependencies and >>>>>> keep the order between atomic states. Cancelling the outstanding >>>>>> modesets, replacing with a disable and then on restore jumping to the >>>>>> final state look doable. It also requires avoiding the struct_mutex for >>>>>> disabling, which is quite easy. To avoid the wait under struct_mutex, >>>>>> we've talked about switching to mmio, but for starters we could move the >>>>>> wait from inside intel_overlay into the fence for the atomic operation. >>>>>> (But's that a little more surgery than we would like for intel_overlay I >>>>>> guess - dig out Ville's patches for overlay planes?) And to prevent the >>>>>> wait under struct_mutex for pin_to_display_plane, my plane is to move >>>>>> that to an async fenced operation that is then naturally waited upon by >>>>>> the atomic modeset. >>>>> A bit more a hack, but a different idea, and I think hack for gen234.0 is >>>>> ok: >>>>> >>>>> We complete all the requests before we start the hw reset with fence.error >>>>> = -EIO. But we do this only when we need to get at the display locks. A >>>>> slightly more elegant solution would be to trylock modeset locks, and if >>>>> one of them fails (and only then) complete all requests with -EIO to get >>>>> the concurrent modeset to proceed before we reset the hardware. That's >>>>> essentially the logic we had before all the reworks, and it worked. But I >>>>> didn't look at how scary that all would be to make it work again ... >>>> The modeset lock may not just be waiting on our requests (even on pnv we >>>> can expect that there are already users celebrating that pnv+nouveau >>>> finally works ;) and that the display is not the only user/observer of >>>> those requests. Using the requests to break the modeset lock just feels >>>> like the wrong approach. >>> It's a cycle, and we need to break it somewhere. Another option might be >>> to break the cycle the same way we do it for gem locks: Wake up everyone >>> and restart the modeset ioctl. Since the trouble only happens for >>> synchronous modesets where we hold the locks while waiting for fences, we >>> can also break out of that and restart. And I also don't think that would >>> leak to other drivers, after all our gem locking restart dances also don't >>> leak to other drivers - it's just our own driver's lock which are affected >>> by these special wakupe semantics. >> It's a queue of nonblocking modesets that we need to worry about, afaik. >> Moving the wait for blocking modeset outside of modeset lock is easily >> achievable (and avoiding the other waits under both the modeset + >> struct_mutex I have at least an idea for). So the challenge is how to >> inject all-planes-off for gen3 and then allow the queue to continue again >> afterwards. > Hm right, I missed the nonblocking updates which don't take locks. But > assuming we do the display reset for gpu resets as a full modeset (i.e. > going through ->atomic_commit) it should still work out correctly: > > Starting state: gpu is hung, nonblocking modeset waiting for some requests > to complete. Missing one evil detail here, else things would have moved forward.. A unrelated thread performs a blocking commit, and holds all locks until the nonblocking modeset completes. > 1. hangcheck kicks in, fires off reset work. > > 2. We complete all requests with fence.error = -EIO and wake up any > waiters. That means no re-queueing for older platforms, but oh well. > > 3. We grab all the display locks. Nothing happens yet. > > 4. We reset the chip, display dies. > > 5. We run ->atomic_commit to restore things. This will also force the > nonblocking commit worker to complete before this display restore touches > anything. > > The only trouble I see is that the nonblocking worker can still touch the > display block while we kill it, which isn't awesome. But we can fix that > by waiting for all pending nonblocking commits in step 3 manually (without > calling into atomic_commit), as long as we do step 2. > > So completing everything with EIO unconditionally still seems like the > simplest option that actually works for pre-g4x ... > -Daniel _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
