On 11/03/2015 16:44, Jesse Barnes wrote:
On 03/11/2015 09:14 AM, Daniel Vetter wrote:
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.Harrison@xxxxxxxxx wrote:
From: John Harrison <John.C.Harrison@xxxxxxxxx>
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.Harrison@xxxxxxxxx>
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
I don't think the space calculation bug could cause the gem_ringfill
failure. As noted above, even when the calculation gets it horribly
wrong and flunks the wait for request path, the sit and poll path should
still do the right thing. Plus the 88865 bug report I've already tried
to reproduce and verified as fixed by the initial version of this patch
set (i.e. without the space calc bug fix or the clean up of the fake
request that follows it). It would go wrong pretty reliably on a clean
nightly but never failed on my anti-OLR branch after quite a large
amount of trying.
I've just realised that I somehow got completely the wrong bug number in
the cover letter. So where patch zero talks about fixing a gem_ringfill
bug, it was supposed to be BZ:88865 not BZ:4####! The second one,
BZ:89001 certainly looks like the same issue but I don't have a SKL to
test with.
Can you please check whether your fixes help for those issues two?
Also adding Jesse since he's chasing these atm.
Ah cool, sounds related at least. 89001 was the one I looked at
yesterday. The worrying thing was that this bug caused a hard system
hang. Not even the reset button worked... I guess we should have an
HSD for that too so we can root cause the system part of it.
Jesse
_______________________________________________
Intel-gfx mailing list
Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
http://lists.freedesktop.org/mailman/listinfo/intel-gfx
