From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([140.186.70.92]:38116) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1R235m-00065A-IF for qemu-devel@nongnu.org; Fri, 09 Sep 2011 11:34:11 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1R235l-0003nO-H8 for qemu-devel@nongnu.org; Fri, 09 Sep 2011 11:34:10 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45650) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1R235l-0003mk-AI for qemu-devel@nongnu.org; Fri, 09 Sep 2011 11:34:09 -0400 Message-ID: <4E6A31E5.3070208@redhat.com> Date: Fri, 09 Sep 2011 17:33:57 +0200 From: Paolo Bonzini MIME-Version: 1.0 References: <1315495505-28906-1-git-send-email-pbonzini@redhat.com> <1315495505-28906-13-git-send-email-pbonzini@redhat.com> <4E6A2823.9080103@bytemark.co.uk> In-Reply-To: <4E6A2823.9080103@bytemark.co.uk> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 12/12] nbd: split requests List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Nicholas Thomas Cc: kwolf@redhat.com, qemu-devel@nongnu.org On 09/09/2011 04:52 PM, Nicholas Thomas wrote: >> > +/* qemu-nbd has a limit of slightly less than 1M per request. For safety, >> > + * transfer at most 512K per request. */ >> > +#define NBD_MAX_SECTORS 1024 > > As far as I'm aware, the limit of 1MiB - header size is common to all > NBD servers. I'm not aware of anything at all that'll fail on a 768K > request but succeed in the exact same circumstances on a 512K request. > Again, this is a performance consideration - each request is relatively > slow, so you don't want them to be unnecessarily small. Yes, it should probably be bumped to 1536 or 2040 (to keep requests 4k-aligned). I wasn't sure about the limit. I've never seen requests that big anyway. Paolo