From mboxrd@z Thu Jan 1 00:00:00 1970 From: Badari Pulavarty Subject: Re: [RFC] vhost-blk implementation Date: Thu, 25 Mar 2010 07:36:45 -0700 Message-ID: <4BAB74FD.2090009@us.ibm.com> References: <1269306023.7931.72.camel@badari-desktop> <20100324200402.GA22272@infradead.org> <4BAA748D.40509@us.ibm.com> <4BAB1765.2070707@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Christoph Hellwig , kvm@vger.kernel.org To: Avi Kivity Return-path: Received: from e6.ny.us.ibm.com ([32.97.182.146]:39396 "EHLO e6.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751863Ab0CYOgg (ORCPT ); Thu, 25 Mar 2010 10:36:36 -0400 Received: from d01relay06.pok.ibm.com (d01relay06.pok.ibm.com [9.56.227.116]) by e6.ny.us.ibm.com (8.14.3/8.13.1) with ESMTP id o2PEXoeU012073 for ; Thu, 25 Mar 2010 10:33:50 -0400 Received: from d01av04.pok.ibm.com (d01av04.pok.ibm.com [9.56.224.64]) by d01relay06.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id o2PEaV191315032 for ; Thu, 25 Mar 2010 10:36:32 -0400 Received: from d01av04.pok.ibm.com (loopback [127.0.0.1]) by d01av04.pok.ibm.com (8.14.3/8.13.1/NCO v10.0 AVout) with ESMTP id o2PEaVeu014040 for ; Thu, 25 Mar 2010 10:36:31 -0400 In-Reply-To: <4BAB1765.2070707@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: Avi Kivity wrote: > On 03/24/2010 10:22 PM, Badari Pulavarty wrote: >>> Which caching mode is this? I assume data=writeback, because otherwise >>> you'd be doing synchronous I/O directly from the handler. >> >> >> Yes. This is with default (writeback) cache model. As mentioned >> earlier, readhead is helping here >> and most cases, data would be ready in the pagecache. > > > btw, relying on readahead is problematic. The guest already issues > readahead requests, and the host will issue readahead based on that > readahead, reading far into the future. > Sure. In my tests, I did O_DIRECT in the guest - so there is no readahead in the guest. Thanks, Badari