linux-kernel - Re: frequent lockups in 3.18rc4

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Date:	Fri, 21 Nov 2014 11:52:27 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	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 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.

--Andy
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