linux-kernel - Re: [PATCH RESEND 5/5] vhost-blk: Add vhost-blk support

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Date:	Fri, 20 Jul 2012 15:56:19 -0500
From:	Anthony Liguori <anthony@...emonkey.ws>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Asias He <asias@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH RESEND 5/5] vhost-blk: Add vhost-blk support

"Michael S. Tsirkin" <mst@...hat.com> writes:

> On Thu, Jul 19, 2012 at 08:05:42AM -0500, Anthony Liguori wrote:
>> Of course, the million dollar question is why would using AIO in the
>> kernel be faster than using AIO in userspace?
>
> Actually for me a more important question is how does it compare
> with virtio-blk dataplane?

I'm not even asking for a benchmark comparision.  It's the same API
being called from a kernel thread vs. a userspace thread.  Why would
there be a 60% performance difference between the two?  That doesn't
make any sense.

There's got to be a better justification for putting this in the kernel
than just that we can.

I completely understand why Christoph's suggestion of submitting BIOs
directly would be faster.  There's no way to do that in userspace.

Regards,

Anthony Liguori

>
> -- 
> MST
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