linux-kernel - Re: [PATCH UPDATED 1/3] vhost: replace vhost

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Message-ID: <20100726163108.GE26412@redhat.com>
Date:	Mon, 26 Jul 2010 19:31:08 +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 UPDATED 1/3] vhost: replace vhost_workqueue with
 per-vhost kthread

On Mon, Jul 26, 2010 at 06:14:30PM +0200, Tejun Heo wrote:
> Just one more thing.
> 
> On 07/26/2010 06:05 PM, Tejun Heo wrote:
> > * Placing try_to_freeze() could be a bit annoying.  It shouldn't be
> >   executed when there's a work to flush.

BTW why is this important?
We could always get another work and flush right after
try_to_freeze, and then flush would block for a long time.


BTW the vhost patch you sent does not do this at all.
I am guessing it is because our thread is not freezable?

> * Similar issue exists for kthread_stop().  The kthread shouldn't exit
>   while there's a work to flush (please note that kthread_worker
>   interface allows detaching / attaching worker kthread during
>   operation, so it should remain in consistent state with regard to
>   flushing).
> 
> Thanks.

Not sure I agree here. Users must synchronise flush and stop calls.
Otherwise a work might get queued after stop is called, and
you won't be able to flush it.


> -- 
> tejun
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