linux-kernel - Re: frequent lockups in 3.18rc4

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Message-ID: <CALCETrUT3Pn0ZCMsgp9dyDvoaiszCrQRc4159Tyggo5wA6Mp7w@mail.gmail.com>
Date:	Fri, 21 Nov 2014 12:16:34 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Josh Boyer <jwboyer@...oraproject.org>
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 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.

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.

--Andy

>
> josh



-- 
Andy Lutomirski
AMA Capital Management, LLC
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