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

From: Anthony Liguori
Date: Fri Jul 20 2012 - 16:56:17 EST

"Michael S. Tsirkin" <mst@xxxxxxxxxx> 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.


Anthony Liguori

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