From mboxrd@z Thu Jan 1 00:00:00 1970 From: Asias He Subject: Re: [PATCH 1/2] kvm tools: Bring VIRTIO_BLK_F_SEG_MAX feature back to virtio blk Date: Sat, 14 May 2011 00:16:08 +0800 Message-ID: <4DCD5948.6090502@gmail.com> References: <1305254409-9079-1-git-send-email-asias.hejun@gmail.com> <4DCD2833.7080803@cs.helsinki.fi> <1305295673.25256.16.camel@lappy> <4DCD4184.3040803@gmail.com> <1305300399.25256.20.camel@lappy> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: Pekka Enberg , Cyrill Gorcunov , Ingo Molnar , Prasad Joshi , kvm@vger.kernel.org To: Sasha Levin Return-path: Received: from mail-pv0-f174.google.com ([74.125.83.174]:45351 "EHLO mail-pv0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753337Ab1EMQRY (ORCPT ); Fri, 13 May 2011 12:17:24 -0400 Received: by pvg12 with SMTP id 12so1214359pvg.19 for ; Fri, 13 May 2011 09:17:24 -0700 (PDT) In-Reply-To: <1305300399.25256.20.camel@lappy> Sender: kvm-owner@vger.kernel.org List-ID: On 05/13/2011 11:26 PM, Sasha Levin wrote: > On Fri, 2011-05-13 at 22:34 +0800, Asias He wrote: >> On 05/13/2011 10:07 PM, Sasha Levin wrote: >>> On Fri, 2011-05-13 at 15:46 +0300, Pekka Enberg wrote: >>>> On 5/13/11 5:40 AM, Asias He wrote: >>>>> commit b764422bb0b46b00b896f6d4538ac3d3dde9e56b >>>>> (kvm tools: Add support for multiple virtio-blk) >>>>> removed the VIRTIO_BLK_F_SEG_MAX publishment to guest. >>>>> >>>>> There is no reason we should not support it. Just bring it back. >>>>> >>>>> Signed-off-by: Asias He >>>> >>>> Sasha? >>> >>> I'm not sure why it was removed, must have missed it when updating >>> struct blk_dev. >>> >>> On the other hand, why do we need to limit max segment size? >> >> That's because the number of entries in a scatter-gather operation must >> be less than the entries in the virt queue we can offer. >> > > I thought that since it's the guest who allocates vq buffers and it's > the guest who does the sg ops, it won't attempt to do that. The size of the virt queue (number of entries) is determined by the device (host). > > But if thats the concern, then yes - lets add it to be safe. > -- Best Regards, Asias He