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Message-ID: <154201973877.16646.5745251436337959698@skylake-alporthouse-com>
Date: Mon, 12 Nov 2018 10:48:58 +0000
From: Chris Wilson <chris@...is-wilson.co.uk>
To: "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
Christian König <ckoenig.leichtzumerken@...il.com>,
Eric Anholt <eric@...olt.net>, christian.koenig@....com,
zhoucm1 <zhoucm1@....com>
Cc: Daniel Vetter <daniel.vetter@...ll.ch>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] drm: Revert syncobj timeline changes.
Quoting Christian König (2018-11-12 10:16:01)
> Am 09.11.18 um 23:26 schrieb Eric Anholt:
>
> Eric Anholt <eric@...olt.net> writes:
>
>
> [ Unknown signature status ]
> zhoucm1 <zhoucm1@....com> writes:
>
>
> On 2018年11月09日 00:52, Christian König wrote:
>
> Am 08.11.18 um 17:07 schrieb Koenig, Christian:
>
> Am 08.11.18 um 17:04 schrieb Eric Anholt:
>
> Daniel suggested I submit this, since we're still seeing regressions
> from it. This is a revert to before 48197bc564c7 ("drm: add syncobj
> timeline support v9") and its followon fixes.
>
> This is a harmless false positive from lockdep, Chouming and I are
> already working on a fix.
>
> On the other hand we had enough trouble with that patch, so if it
> really bothers you feel free to add my Acked-by: Christian König
> <christian.koenig@....com> and push it.
>
> NAK, please no, I don't think this needed, the Warning totally isn't
> related to syncobj timeline, but fence-array implementation flaw, just
> exposed by syncobj.
> In addition, Christian already has a fix for this Warning, I've tested.
> Please Christian send to public review.
>
> I backed out my revert of #2 (#1 still necessary) after adding the
> lockdep regression fix, and now my CTS run got oomkilled after just a
> few hours, with these notable lines in the unreclaimable slab info list:
>
> [ 6314.373099] drm_sched_fence 69095KB 69095KB
> [ 6314.373653] kmemleak_object 428249KB 428384KB
> [ 6314.373736] kmalloc-262144 256KB 256KB
> [ 6314.373743] kmalloc-131072 128KB 128KB
> [ 6314.373750] kmalloc-65536 64KB 64KB
> [ 6314.373756] kmalloc-32768 1472KB 1728KB
> [ 6314.373763] kmalloc-16384 64KB 64KB
> [ 6314.373770] kmalloc-8192 208KB 208KB
> [ 6314.373778] kmalloc-4096 2408KB 2408KB
> [ 6314.373784] kmalloc-2048 288KB 336KB
> [ 6314.373792] kmalloc-1024 1457KB 1512KB
> [ 6314.373800] kmalloc-512 854KB 1048KB
> [ 6314.373808] kmalloc-256 188KB 268KB
> [ 6314.373817] kmalloc-192 69141KB 69142KB
> [ 6314.373824] kmalloc-64 47703KB 47704KB
> [ 6314.373886] kmalloc-128 46396KB 46396KB
> [ 6314.373894] kmem_cache 31KB 35KB
>
> No results from kmemleak, though.
>
> OK, it looks like the #2 revert probably isn't related to the OOM issue.
> Running a single job on otherwise unused DRM, watching /proc/slabinfo
> every second for drm_sched_fence, I get:
>
> drm_sched_fence 0 0 192 21 1 : tunables 32 16 8 : slabdata 0 0 0 : globalstat 0 0 0 0 0 0 0 0 0 : cpustat 0 0 0 0
> drm_sched_fence 16 21 192 21 1 : tunables 32 16 8 : slabdata 1 1 0 : globalstat 16 16 1 0 0 0 0 0 0 : cpustat 5 1 6 0
> drm_sched_fence 13 21 192 21 1 : tunables 32 16 8 : slabdata 1 1 0 : globalstat 16 16 1 0 0 0 0 0 0 : cpustat 5 1 6 0
> drm_sched_fence 6 21 192 21 1 : tunables 32 16 8 : slabdata 1 1 0 : globalstat 16 16 1 0 0 0 0 0 0 : cpustat 5 1 6 0
> drm_sched_fence 4 21 192 21 1 : tunables 32 16 8 : slabdata 1 1 0 : globalstat 16 16 1 0 0 0 0 0 0 : cpustat 5 1 6 0
> drm_sched_fence 2 21 192 21 1 : tunables 32 16 8 : slabdata 1 1 0 : globalstat 16 16 1 0 0 0 0 0 0 : cpustat 5 1 6 0
> drm_sched_fence 0 21 192 21 1 : tunables 32 16 8 : slabdata 0 1 0 : globalstat 16 16 1 0 0 0 0 0 0 : cpustat 5 1 6 0
>
> So we generate a ton of fences, and I guess free them slowly because of
> RCU? And presumably kmemleak was sucking up lots of memory because of
> how many of these objects were laying around.
>
>
> That is certainly possible. Another possibility is that we don't drop the
> reference in dma-fence-array early enough.
>
> E.g. the dma-fence-array will keep the reference to its fences until it is
> destroyed, which is a bit late when you chain multiple dma-fence-array objects
> together.
>
> David can you take a look at this and propose a fix? That would probably be
> good to have fixed in dma-fence-array separately to the timeline work.
Note that drm_syncobj_replace_fence() leaks any existing fence for
!timeline syncobjs. Which coupled with the linear search ends up with
a severe regression in both time and memory.
-Chris
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