From mboxrd@z Thu Jan 1 00:00:00 1970 From: "=?utf-8?B?WmhhbmcgSGFveXU=?=" Subject: =?utf-8?B?UmU6IFNvbWUgbW9yZSBiYXNpYyBxdWVzdGlvbnMuLg==?= Date: Tue, 3 Jun 2014 14:47:11 +0800 Message-ID: <201406031447098993964@sangfor.com> References: , <201405291445129559886@sangfor.com>, , <201405301448239589273@sangfor.com>, , <201406031143173652147@sangfor.com>, Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Cc: "=?utf-8?B?a3Zt?=" To: "=?utf-8?B?TWFyY3VzIFdoaXRl?=" Return-path: Received: from smtp.sanfor.com ([58.251.49.30]:53114 "EHLO mail.sangfor.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1752525AbaFCGri (ORCPT ); Tue, 3 Jun 2014 02:47:38 -0400 Sender: kvm-owner@vger.kernel.org List-ID: >>>1. If IO to a block device goes through QEMU and not vhost, are there >>>data copies between kernel and user mode if I do IO to a block device >>>or is it zero copy? Kind of related to Question (2) also. >>> >> I'm not sure, it perhaps depend on which IO mode you chose, qemu pthreads IO, or linux AIO? >> Somebody else do a favour, please. > >That would be definitely good to know:) I didnt know about the modes >as such. Can you clarify? Are you talking about vhost-LIO vs Qemu? The >LIO part, I do believe, is zero copy.. >I have seen pretty high memory usage on QEMU thread, not sure why. > Sorry for my poor knowledge about block subsystem. I don't know about vhost-LIO, do you mean vhost-blk or vhost-scsi? Linux AIO what I said above is the linux native aio, which only works for uncached access(O_DIRECT), qemu main-thread use it to do block IO, qemu pthreads IO means that qemu creates dedicated threads to do block IO job.