On Wed, Jun 12, 2013 at 12:28 PM, Terje Bergström <tbergstrom@xxxxxxxxxx> wrote: > On 11.06.2013 15:09, Daniel Vetter wrote: >> Maybe it wasn't clear, but -EAGAIN does _not_ resubmit work. -EAGAIN >> is used to restart the ioctl if we had to kick a thread (to make sure >> it doesn't hold any locks), e.g. for a blocking wait on oustanding >> rendering. The codepaths taken work exactly as if the thread is >> interrupt with a signal. > > You did make it clear that there's no resubmission, but other parts > confused me. > > So this is used so that a legacy driver which does not do fine-grained > locking can interrupt all waits for completion for a wedged submit. This > way a driver-wide lock get unlocked, cleanup code acquires locks, does > the magic to unwedge GPU, and unlocks. Then user space can re-submit the > waits as it got -EAGAIN. I think this is not just for drivers without fine-grained locking, at least I expect that we'll keep the same mechanism when switching over to per-object locking - we simply have too many places where a thread could arbitrarily block while holding locks that the gpu reset handler also needs to grab. You could of course restructure the code massively and drop all locks while waiting, but that means adding tons of special-purpose code which is only really exercises when a gpu hang occurs. Our approach with the ioctl restart otoh reuses codepaths which are all heavily used by X (due to X constantly getting interrupt by timers and input events). -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
