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

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Message-ID: <20100726162346.GD26412@redhat.com>
Date:	Mon, 26 Jul 2010 19:23:46 +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 06:05:27PM +0200, Tejun Heo wrote:
> Hello,
> 
> On 07/26/2010 05:50 PM, Michael S. Tsirkin wrote:
> >> Hmmm... I'm not quite sure whether it's an optimization.  I thought
> >> the patch was due to feeling uncomfortable about using barriers?
> > 
> > Oh yes. But getting rid of barriers is what motivated me originally.
> 
> Yeah, getting rid of barriers is always good.  :-)
> 
> > Is there a git tree with kthread_worker applied?
> > I might do this just for fun ...
> 
>  git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq.git for-next
> 
> For the original implementaiton, please take a look at commit
> b56c0d8937e665a27d90517ee7a746d0aa05af46.
> 
> * Can you please keep the outer goto repeat loop?  I just don't like
>   outermost for (;;).

Okay ... can we put the code in a {} scope to make it clear
where does the loop starts and ends?

> * Placing try_to_freeze() could be a bit annoying.  It shouldn't be
>   executed when there's a work to flush.

It currently seems to be executed when there is work to flush.
Is this wrong?

> * I think A - B <= 0 test would be more familiar.  At least
>   time_before/after() are implemented that way.

I am concerned that this overflows a signed integer -
which I seem to remeber that C99 disallows.
timer macros are on data path so might be worth the risk there,
but flush is slow path so better be safe?

> Thanks.
> 
> -- 
> tejun
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