linux-kernel - Re: frequent lockups in 3.18rc4

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Message-ID: <CAAJw_ZsQBeMRXgrM8CHS9FPTEk_fJYkqWm6NJpgrBGdY=_X6Tw@mail.gmail.com>
Date:	Sun, 14 Dec 2014 00:28:33 +0800
From:	Jeff Chua <jeff.chua.linux@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Sasha Levin <sasha.levin@...cle.com>,
	Dave Jones <davej@...hat.com>, Chris Mason <clm@...com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Dâniel Fraga <fragabr@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: frequent lockups in 3.18rc4

I started seeing this behavior somewhere around 3.16 with
CONFIG_PREEMPT set. Setting CONFIG_PREEMPT off seems to help. And,
yes, it happens on high load (compiling mozilla, xul) and using qemu
chroot to compile mesa.

I'm seeing a few persons bisecting already. If you want, I could start
bisecting too, but 3.16 was unstable for me as I'm still on reiserfs.

Jeff.



On Sat, Dec 13, 2014 at 8:44 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Fri, Dec 12, 2014 at 4:34 PM, Sasha Levin <sasha.levin@...cle.com> wrote:
>>
>> Right, it's virtio-9p. However, virtio-9p acts merely as a proxy to an underlying
>> tmpfs - so while it's slow, I don't think it's way slower than the average disk
>> backed ext4.
>
> I was thinking more in the sense of "how much of the trouble is about
> something like tmpfs eating tons of memory when trinity starts doing
> random system calls on those files".
>
> I was also thinking that some of it might be filesystem-specific. We
> already *did* see one trace where it was in the loop getting virtio
> channel data. Maybe it's actually possible to overwhelm the 9p
> filesystem exactly because the backing store is tmpfs, and basically
> have a CPU 100% busy handling ring events from the virtual
> filesystem..
>
> But I'm just flailing..
>
>                      Linus
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