From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [RFC] vhost-blk implementation Date: Mon, 29 Mar 2010 23:37:09 +0300 Message-ID: <4BB10F75.2000701@redhat.com> References: <1269306023.7931.72.camel@badari-desktop> <20100324200402.GA22272@infradead.org> <1269877312.7931.93.camel@badari-desktop> <20100329182010.GM1744@sequoia.sous-sol.org> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Badari Pulavarty , Christoph Hellwig , kvm@vger.kernel.org To: Chris Wright Return-path: Received: from mx1.redhat.com ([209.132.183.28]:1401 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753296Ab0C2Uh1 (ORCPT ); Mon, 29 Mar 2010 16:37:27 -0400 In-Reply-To: <20100329182010.GM1744@sequoia.sous-sol.org> Sender: kvm-owner@vger.kernel.org List-ID: On 03/29/2010 09:20 PM, Chris Wright wrote: > * Badari Pulavarty (pbadari@us.ibm.com) wrote: > >> I modified my vhost-blk implementation to offload work to >> work_queues instead of doing synchronously. Infact, I tried >> to spread the work across all the CPUs. But to my surprise, >> this did not improve the performance compared to virtio-blk. >> >> I see vhost-blk taking more interrupts and context switches >> compared to virtio-blk. What is virtio-blk doing which I >> am not able to from vhost-blk ??? >> > Your io wait time is twice as long and your throughput is about half. > I think the qmeu block submission does an extra attempt at merging > requests. Does blktrace tell you anything interesting? > It does. I suggest using fio O_DIRECT random access patterns to avoid such issues. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic.