linux-kernel - Re: vhost threading model

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Message-Id: <201603231114.u2NBE1As012130@d06av04.portsmouth.uk.ibm.com>
Date:	Wed, 23 Mar 2016 13:13:55 +0200
From:	"Michael Rapoport" <RAPOPORT@...ibm.com>
To:	Bandan Das <bsd@...hat.com>
Cc:	jiangshanlai@...il.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, mst@...hat.com, tj@...nel.org
Subject: Re: vhost threading model

> Bandan Das <bsd@...hat.com> wrote on 03/22/2016 09:00:50 PM:
> > "Michael Rapoport" <RAPOPORT@...ibm.com> writes:
> >
> > Well, Elvis is a _theoretical_ example that showed that I/O scheduling 
in 
> > the vhost improves performance.
> > I'm not saying we should take Evlis and try to squeeze it into the 
vhost, 
> > I just want to say that we cannot switch vhost to use workqueues if it 

> > causes performance degradation.
> >
> > My opinion is that we need to give it some more thought, much more 
> > performance evaluation, so that we can find the best model.
> 
> Exactly, I think we are outright discarding using workqueues even
> without investigating it in detail even though it would be a cleaner
> implementation using a common framework and thereby more chances of
> an acceptable solution for upstream.

I'm not suggesting to discard using workqueues.
All I'm saying that among several options for vhost threading model we 
should find the one with best "performance/complexity" ratio :)
 
> Anyway, if we don't want to go the workqueues way for vhost, cgroups
> support for workqueues is still something worth having on its own.

No objection to that.
 
> >> > opportunity for optimization, at least for some workloads...
> >> > That said, I believe that switching vhost to use workqueues is not 
> > that 
> >> > good idea after all.
> >> > 
> >