On Wed, Mar 11, 2015 at 02:53:39PM +0000, John Harrison wrote: > On 05/03/2015 14:49, Daniel Vetter wrote: > >On Thu, Mar 05, 2015 at 01:57:31PM +0000, john.c.harri...@intel.com wrote: > >>From: John Harrison <john.c.harri...@intel.com> > >> > >>The LRC submission code requires a request for tracking purposes. It does > >>not > >>actually require that request to 'complete' it simply uses it for keeping > >>hold > >>of reference counts on contexts and such like. > >> > >>In the case where the ring buffer is completely full, the LRC code looks > >>for a > >>pending request that would free up sufficient space upon completion and > >>waits > >>for it. If no such request can be found it resorts to simply polling the > >>free > >>space count until it is big enough. This situation should only occur when > >>the > >>entire buffer is filled with the request currently being generated. I.e., > >>the > >>user is trying to submit a single piece of work that is large than the ring > >>buffer itself (which should be impossible because very large batch buffers > >>don't > >>consume any more ring buffer space). Before starting to poll, a submit call > >>is > >>made to make sure that the currently queued up work in the buffer will > >>actually > >>be submtted and thus the poll will eventually succeed. > >> > >>The problem here is that the 'official' request cannot be used as that could > >>lead to multiple LRC submissions being tagged to a single request structure. > >>Instead, the code fakes up a private request structure and uses that. > >> > >>This patch moves the faked request allocation higher up in the call stack > >>to the > >>wait code itself (rather than being at the very lowest submission level). > >>Thus > >>it is now obvious where the faked request is coming from and why it is > >>necessary. The patch also replaces it with a call to the official request > >>allocation code rather than attempting to duplicate that code. This becomes > >>especially important in the future when the request allocation changes to > >>accommodate a conversion to struct fence. > >> > >>For: VIZ-5115 > >>Signed-off-by: John Harrison <john.c.harri...@intel.com> > >This is only possible if you pile up tons of olr. Since your patch series > >fixes this design issue by removing olr I think we can just put a WARN_ON > >in here if this ever happens and bail out with -ELOSTMYMARBLES or > >something. And then rip out all this complexity. > > > >Or do I miss something important? > >-Daniel > > Yeah, you missed the extremely important bug in the free space calculation > that meant this impossible code path was being hit on a regular basis. The > LRC wait_request code differed from the legacy wait_request code in the the > latter was updated with request->postfix changes and the former was not. > Thus the LRC one would happily find a request that frees up enough space, > wait on it, retire it and then find there was still not enough space! > > New patches to fix the space calculation bug and to completely remove the > polling path will be forth coming...
Hm, Jesse did dig out a regression where gem_ringfill blows up on execlist. That igt is specifically to exercise this cornercases. I'm not sure whith bugzilla Jesse meant, there's two: https://bugs.freedesktop.org/show_bug.cgi?id=89001 https://bugs.freedesktop.org/show_bug.cgi?id=88865 Can you please check whether your fixes help for those issues two? Also adding Jesse since he's chasing these atm. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/intel-gfx
