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Date: Mon, 11 Jan 2010 08:00:57 -0600
From: Anthony Liguori <anthony@codemonkey.ws>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] Re: [RFC][PATCH] performance improvement for windows
	guests, running on top of virtio block device
References: <1263195647.2005.44.camel@localhost>
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To: Christoph Hellwig <hch@lst.de>
Cc: qemu-devel <qemu-devel@nongnu.org>, Dor Laor <dlaor@redhat.com>, Avi Kivity <avi@redhat.com>, Vadim Rozenfeld <vrozenfe@redhat.com>

On 01/11/2010 07:47 AM, Christoph Hellwig wrote:
> On Mon, Jan 11, 2010 at 03:13:53PM +0200, Avi Kivity wrote:
>    
>> As Dor points out, the call to virtio_blk_handle_output() wants to be
>> before the test for pending, so we scan the ring as early as possible
>>      
> It could cause a race window where we add an entry to the ring after
> we run virtio_blk_handle_output, but before re-enabling the
> notification.  But I think my variant of the patch that I just posted
> should deal with this in an even better way.
>    

When we've disabled notifications, we should use any opportunity we have 
in userspace to check the rings to see if anything was added.

Bottom halves are run at the very end of the event loop which means that 
they're guaranteed to be the last thing run.  idle bottom halves can be 
rescheduled without causing an infinite loop and do not affect the 
select timeout (which normal bottom halves do).

Regards,

Anthony Liguori

>
>