From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751296AbeDDO1s (ORCPT ); Wed, 4 Apr 2018 10:27:48 -0400 Received: from mga02.intel.com ([134.134.136.20]:63393 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751167AbeDDO1r (ORCPT ); Wed, 4 Apr 2018 10:27:47 -0400 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.48,406,1517904000"; d="scan'208";a="30650430" Date: Wed, 4 Apr 2018 08:30:27 -0600 From: Keith Busch To: "Eric H. Chang" Cc: Christoph Hellwig , Baegjae Sung , "axboe@fb.com" , "sagi@grimberg.me" , "linux-nvme@lists.infradead.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] nvme-multipath: implement active-active round-robin path selector Message-ID: <20180404143027.GE4485@localhost.localdomain> References: <20180327043851.6640-1-baegjae@gmail.com> <20180328080646.GB20373@lst.de> <20180328194741.GJ13039@localhost.localdomain> <20180330070651.GA17095@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 30, 2018 at 09:04:46AM +0000, Eric H. Chang wrote: > We internally call PCIe-retimer as HBA. It's not a real Host Bus Adapter that translates the interface from PCIe to SATA or SAS. Sorry for the confusion. Please don't call a PCIe retimer an "HBA"! :) While your experiment is setup to benefit from round-robin, my only concern is it has odd performance in a real world scenario with IO threads executing in different nodes. Christoph's proposal will naturally utilize both paths optimally there, where round-robin will saturate node interlinks. Not that I'm against having the choice; your setup probably does represent real use. But if we're going to have multiple choice, user documentation on nvme path selectors will be useful here.