lkml.org 
[lkml]   [2015]   [Feb]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v2 0/5] rcu,nohz,kvm: use RCU extended quiescent state when running KVM guest
On Fri, Feb 06, 2015 at 02:50:44PM +0100, Paolo Bonzini wrote:
>
>
> On 06/02/2015 14:46, Frederic Weisbecker wrote:
> > > When running a KVM guest on a system with NOHZ_FULL enabled
> >
> > I just need to clarify the motivation first, does the above situation
> > really happen? Ok some distros enable NOHZ_FULL to let the user stop
> > the tick in userspace. So most of the time, CONFIG_NOHZ_FULL=y but
> > nohz full is runtime disabled (we need to pass a nohz_full= boot
> > parameter to enable it). And when it is runtime disabled, there should
> > be no rcu nocb CPU.
> >
> > (Although not setting CPUs in nocb mode when nohz full is runtime disabled
> > is perhaps a recent change.)
> >
> > So for the problem to arise, one need to enable nohz_full and run KVM
> > guest. And I never heard about such workloads.
>
> Yeah, it's a new thing but Marcelo, Luiz and Rik have been having a lot
> of fun with them (with PREEMPT_RT too). They're getting pretty good
> results given the right tuning.
>
> I'll let Paul queue the patches for 3.21 then!

Frederic, given the background from Paolo, Rik, and Christian, are you
OK with these patches?

Thanx, Paul

> Paolo
>
> > That said it's potentially
> > interesting to turn off the tick on the host when the guest runs.
>



\
 
 \ /
  Last update: 2015-02-06 17:41    [W:0.157 / U:0.456 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site