From: Asias He <asias@redhat.com>
To: Anthony Liguori <anthony@codemonkey.ws>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
virtualization@lists.linux-foundation.org
Subject: Re: [PATCH RESEND 5/5] vhost-blk: Add vhost-blk support
Date: Sat, 21 Jul 2012 09:07:57 +0800 [thread overview]
Message-ID: <500A00ED.9090508@redhat.com> (raw)
In-Reply-To: <87obnaup70.fsf@codemonkey.ws>
On 07/21/2012 04:56 AM, Anthony Liguori wrote:
> "Michael S. Tsirkin" <mst@redhat.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.
Please read the commit log again. I am not saying vhost-blk v.s
userspace implementation gives 60% improvement. I am saying the
vhost-blk v.s original vhost-blk gives 60% improvement.
"""
This patch is based on Liu Yuan's implementation with various
improvements and bug fixes. Notably, this patch makes guest notify and
host completion processing in parallel which gives about 60% performance
improvement compared to Liu Yuan's implementation.
"""
>
> 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.
Well. With Zach and Dave's new in-kernel aio API, the aio usage in
kernel is much simpler than in userspace. This a potential reason that
in kernel one is better than userspace one. I am working on it right
now. And for block based image, as suggested by Christoph, we can submit
bio directly. This is another potential reason.
Why can't we just go further to see if we can improve the IO stack from
guest kernel side all the way down to host kernel side. We can not do
that if we stick to doing everything in userspace (qemu).
--
Asias
next prev parent reply other threads:[~2012-07-21 1:06 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-13 8:55 [PATCH RESEND 0/5] Add vhost-blk support Asias He
2012-07-13 8:55 ` [PATCH RESEND 1/5] aio: Export symbols and struct kiocb_batch for in kernel aio usage Asias He
2012-07-13 8:55 ` [PATCH RESEND 2/5] eventfd: Export symbol eventfd_file_create() Asias He
2012-07-13 8:55 ` [PATCH RESEND 3/5] vhost: Make vhost a separate module Asias He
2012-07-13 8:55 ` [PATCH RESEND 4/5] vhost-net: Use VHOST_NET_FEATURES for vhost-net Asias He
2012-07-13 8:55 ` [PATCH RESEND 5/5] vhost-blk: Add vhost-blk support Asias He
2012-07-17 19:10 ` Jeff Moyer
2012-07-18 1:22 ` Asias He
2012-07-18 14:31 ` Jeff Moyer
2012-07-18 14:45 ` Asias He
2012-07-19 13:05 ` Anthony Liguori
2012-07-19 13:09 ` Michael S. Tsirkin
2012-07-19 13:09 ` Michael S. Tsirkin
2012-07-20 10:31 ` Stefan Hajnoczi
2012-07-20 20:56 ` Anthony Liguori
2012-07-21 1:07 ` Asias He [this message]
2012-07-14 7:49 ` [PATCH RESEND 0/5] " Christoph Hellwig
2012-07-16 9:05 ` Asias He
2012-07-17 15:09 ` Michael S. Tsirkin
2012-07-18 2:09 ` Asias He
2012-07-18 11:42 ` Stefan Hajnoczi
2012-07-20 19:30 ` Michael S. Tsirkin
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