linux-kernel - Re: [PATCH 2/3] workqueue: Add an API to create a singlethread workqueue attached to the current task's cgroup

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Message-ID: <20100530112925.GB27611@redhat.com>
Date:	Sun, 30 May 2010 14:29:25 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Sridhar Samudrala <sri@...ibm.com>,
	netdev <netdev@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dmitri Vorobiev <dmitri.vorobiev@...ial.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 2/3] workqueue: Add an API to create a singlethread
	workqueue attached to the current task's cgroup

On Fri, May 28, 2010 at 05:54:42PM +0200, Tejun Heo wrote:
> Hello,
> 
> On 05/28/2010 05:08 PM, Michael S. Tsirkin wrote:
> > Well, we have create_singlethread_workqueue, right?
> > This is not very different ... is it?
> > 
> > Just copying structures and code from workqueue.c,
> > adding vhost_ in front of it will definitely work:
> 
> Sure it will, but you'll probably be able to get away with much less.
> 
> > there is nothing magic about the workqueue library.
> > But this just involves cut and paste which might be best avoided.
> 
> What I'm saying is that some magic needs to be added to workqueue and
> if you add this single(!) exception, it will have to be backed out
> pretty soon, so it would be better to do it properly now.
> 
> > One final idea before we go the cut and paste way: how about
> > 'create_workqueue_from_task' that would get a thread and have workqueue
> > run there?
> 
> You can currently depend on that implementation detail but it's not
> the workqueue interface is meant to do.  The single threadedness is
> there as execution ordering and concurrency specification and it
> doesn't (or rather won't) necessarily mean that a specific single
> thread is bound to certain workqueue.
> 
> Can you please direct me to have a look at the code.  I'll be happy to
> do the conversion for you.

Great, thanks! The code in question is in drivers/vhost/vhost.c
It is used from drivers/vhost/net.c

On top of this, we have patchset from Sridhar Samudrala,
titled '0/3 Make vhost multi-threaded and associate each thread to its
guest's cgroup':

cgroups: Add an API to attach a task to current task's cgroup
workqueue: Add an API to create a singlethread workqueue attached to the
current task's cgroup
vhost: make it more scalable by creating a vhost thread per device

I have bounced the last three your way.


> Thanks.
> 
> -- 
> tejun
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