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

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Message-ID: <4C4FE0CF.3070506@kernel.org>
Date:	Wed, 28 Jul 2010 09:48:31 +0200
From:	Tejun Heo <tj@...nel.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
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 07/27/2010 09:19 PM, Michael S. Tsirkin wrote:
>> Thinking a bit more about it, it kind of sucks that queueing to
>> another worker from worker->func() breaks flush.  Maybe the right
>> thing to do there is using atomic_t for done_seq?
> 
> I don't believe it will help: we might have:
> 
> worker1 runs work
> work requeues itself queued index = 1
> worker1 reads queued index = 1
> worker2 runs work
> work requeues itself queued index = 2
> worker2 runs work
> worker2 reads queued index = 2
> worker2 writes done index = 2
> worker1 writes done index = 1
> 
> As you see, done index got moved back.

Yeah, I think the flushing logic should be moved to the worker.  Are
you interested in doing it w/ your change?

Thanks.

-- 
tejun
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