linux-kernel - Re: frequent lockups in 3.18rc4

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Message-ID: <CALCETrWgS5fitrkGjbu=TNKp2YbNYeS8WBpPvS50Xf1kp116zw@mail.gmail.com>
Date:	Fri, 21 Nov 2014 12:02:19 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Dave Jones <davej@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andy Lutomirski <luto@...capital.net>,
	Tejun Heo <tj@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Don Zickus <dzickus@...hat.com>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Josh Boyer <jboyer@...hat.com>,
	Justin Forbes <jforbes@...hat.com>
Subject: Re: frequent lockups in 3.18rc4

On Fri, Nov 21, 2014 at 12:00 PM, Dave Jones <davej@...hat.com> wrote:
> On Fri, Nov 21, 2014 at 11:46:57AM -0800, Linus Torvalds wrote:
>
>  > 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'm not sure how many people actually use paravirt these days,
> but the reason Fedora has it enabled still at least is probably
> because..
>
> config KVM_GUEST
>          bool "KVM Guest support (including kvmclock)"
>          depends on PARAVIRT
>
> But tbh I've not looked at this stuff since it first got merged.
> Will a full-virt system kvm boot a guest without KVM_GUEST enabled ?
> (ie, is this just an optimisation for the paravirt case?)
>

It will boot just fine, although there may be some timing glitches.

I think we should have PARAVIRT_LITE that's just enough for KVM.  That
probably involves some apic changes and nothing else.

--Andy

> I'm not a heavy virt user, so I don't even remember how a lot of
> this stuff is supposed to work.
>
>         Dave
>



-- 
Andy Lutomirski
AMA Capital Management, LLC
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