From mboxrd@z Thu Jan 1 00:00:00 1970 From: Asias He Subject: Re: [PATCH 0/5] Add vhost-blk support Date: Wed, 18 Jul 2012 16:12:57 +0800 Message-ID: <50067009.9030508@redhat.com> References: <1342107302-28116-1-git-send-email-asias@redhat.com> <50052276.2080906@redhat.com> <500527BA.9000001@redhat.com> <50052E7E.6020100@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Paolo Bonzini , linux-kernel@vger.kernel.org, linux-aio@kvack.org, kvm@vger.kernel.org, "Michael S. Tsirkin" , virtualization@lists.linux-foundation.org, Benjamin LaHaise , Alexander Viro , linux-fsdevel@vger.kernel.org To: Stefan Hajnoczi Return-path: In-Reply-To: Sender: owner-linux-aio@kvack.org List-Id: linux-fsdevel.vger.kernel.org On 07/17/2012 07:11 PM, Stefan Hajnoczi wrote: > On Tue, Jul 17, 2012 at 10:21 AM, Asias He wrote: >> On 07/17/2012 04:52 PM, Paolo Bonzini wrote: >>> >>> Il 17/07/2012 10:29, Asias He ha scritto: >>>> >>>> So, vhost-blk at least saves ~6 syscalls for us in each request. >>> >>> >>> Are they really 6? If I/O is coalesced by a factor of 3, for example >>> (i.e. each exit processes 3 requests), it's really 2 syscalls per request. >> >> >> Well. I am counting the number of syscalls in one notify and response >> process. Sure the IO can be coalesced. > > Linux AIO also supports batching in io_submit() and io_getevents(). > Depending on the request pattern in the vring when you process it, you > should be able to do better than 1 set of syscalls per host I/O > request. > > Are you taking advantage of that at the moment in your userspace benchmark? OK. I know that batching in io_submit() and io_getevetns(). There was a patch for kvm tool long time ago. Now, both vhost-blk and kvm tool are not taking advantage of that atm. There are issues: e.g. How many number of request we want to batch? Does this batching hurt latency? -- Asias -- To unsubscribe, send a message with 'unsubscribe linux-aio' in the body to majordomo@kvack.org. For more info on Linux AIO, see: http://www.kvack.org/aio/ Don't email: aart@kvack.org