From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sasha Levin Subject: Re: [PATCH 1/2] kvm tools: Bring VIRTIO_BLK_F_SEG_MAX feature back to virtio blk Date: Fri, 13 May 2011 18:26:39 +0300 Message-ID: <1305300399.25256.20.camel@lappy> 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> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: Pekka Enberg , Cyrill Gorcunov , Ingo Molnar , Prasad Joshi , kvm@vger.kernel.org To: Asias He Return-path: Received: from mail-ww0-f44.google.com ([74.125.82.44]:55631 "EHLO mail-ww0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752851Ab1EMQDI (ORCPT ); Fri, 13 May 2011 12:03:08 -0400 Received: by wwa36 with SMTP id 36so3036540wwa.1 for ; Fri, 13 May 2011 09:03:06 -0700 (PDT) In-Reply-To: <4DCD4184.3040803@gmail.com> Sender: kvm-owner@vger.kernel.org List-ID: 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. But if thats the concern, then yes - lets add it to be safe. -- Sasha.