From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934131AbcI2Qln (ORCPT ); Thu, 29 Sep 2016 12:41:43 -0400 Received: from latin.grep.be ([46.4.76.168]:60461 "EHLO latin.grep.be" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933829AbcI2Qld (ORCPT ); Thu, 29 Sep 2016 12:41:33 -0400 Date: Thu, 29 Sep 2016 18:41:00 +0200 From: Wouter Verhelst To: Josef Bacik Cc: axboe@fb.com, linux-block@vger.kernel.org, kernel-team@fb.com, nbd-general@lists.sourceforge.net, linux-kernel@vger.kernel.org Subject: Re: [Nbd] [PATCH][V3] nbd: add multi-connection support Message-ID: <20160929164100.akytbkbtvziwaqqj@grep.be> References: <1475092892-8230-1-git-send-email-jbacik@fb.com> <20160929095204.mexr6wpypo3bl6mx@grep.be> <87908d95-0b7c-bc3f-f69d-94d006829daf@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87908d95-0b7c-bc3f-f69d-94d006829daf@fb.com> X-Speed: Gates' Law: Every 18 months, the speed of software halves. Organization: none User-Agent: NeoMutt/20160916 (1.7.0) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 29, 2016 at 10:03:50AM -0400, Josef Bacik wrote: > So think of it like normal disks with multiple channels. We don't send flushes > down all the hwq's to make sure they are clear, we leave that decision up to the > application (usually a FS of course). Well, when I asked earlier, Christoph said[1] that blk-mq assumes that when a FLUSH is sent over one channel, and the reply comes in, that all commands which have been received, regardless of which channel they were received over, have reched disk. [1] Message-ID: <20160915122304.GA15501@infradead.org> It is impossible for nbd to make such a guarantee, due to head-of-line blocking on TCP. [...] > perhaps we could add a flag later that says send all the flushes down > all the connections for the paranoid, it should be relatively > straightforward to do. Thanks, That's not an unreasonable approach, I guess. -- < ron> I mean, the main *practical* problem with C++, is there's like a dozen people in the world who think they really understand all of its rules, and pretty much all of them are just lying to themselves too. -- #debian-devel, OFTC, 2016-02-12