linux-kernel - Re: frequent lockups in 3.18rc4

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Message-ID: <CA+5PVA5L1Vcs+nrJWZ+jXgnhQMZ_L22rksopPnO7Wt04jD3kUQ@mail.gmail.com>
Date:	Fri, 21 Nov 2014 15:23:13 -0500
From:	Josh Boyer <jwboyer@...oraproject.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Tejun Heo <tj@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Don Zickus <dzickus@...hat.com>, Dave Jones <davej@...hat.com>,
	"the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: frequent lockups in 3.18rc4

On Fri, Nov 21, 2014 at 3:16 PM, Andy Lutomirski <luto@...capital.net> wrote:
> On Fri, Nov 21, 2014 at 12:14 PM, Josh Boyer <jwboyer@...oraproject.org> wrote:
>> On Fri, Nov 21, 2014 at 2:52 PM, Andy Lutomirski <luto@...capital.net> wrote:
>>> On Fri, Nov 21, 2014 at 11:46 AM, Linus Torvalds
>>> <torvalds@...ux-foundation.org> wrote:
>>>> On Fri, Nov 21, 2014 at 11:34 AM, Linus Torvalds
>>>> <torvalds@...ux-foundation.org> wrote:
>>>>>
>>>>> So I kind of agree, but it wouldn't be my primary worry. My primary
>>>>> worry is actually paravirt doing something insane.
>>>>
>>>> Btw, on that tangent, does anybody actually care about paravirt any more?
>>>>
>>>
>>> Amazon, for better or for worse.
>>>
>>>> I'd love to start moving away from it. It makes a lot of the low-level
>>>> code completely impossible to follow due to the random indirection
>>>> through "native" vs "paravirt op table". Not just the page table
>>>> handling, it's all over.
>>>>
>>>> Anybody who seriously does virtualization uses hw virtualization that
>>>> is much better than it used to be. And the non-serious users aren't
>>>> that performance-sensitive by definition.
>>>>
>>>> I note that the Fedora kernel config seems to include paravirt by
>>>> default, so you get a lot of the crazy overheads..
>>>
>>> I think that there is a move toward deprecating Xen PV in favor of
>>> PVH, but we're not there yet.
>>
>> A move where?  The Xen stuff in Fedora is ... not paid attention to
>> very much.  If there's something we should be looking at turning off
>> (or on), we're happy to take suggestions.
>
> A move in the Xen project.  As I understand it, Xen wants to deprecate
> PV in favor of PVH, but PVH is still experimental.

OK.

> I think that dropping PARAVIRT in Fedora might be a bad idea for
> several more releases, since that's likely to break the EC2 images.

Yes, that's essentially the only reason we haven't looked at disabling
Xen completely for a while now, so <sad trombone>.

josh
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