From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763978AbdAITqW (ORCPT ); Mon, 9 Jan 2017 14:46:22 -0500 Received: from mail-qk0-f195.google.com ([209.85.220.195]:32866 "EHLO mail-qk0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1763890AbdAITqE (ORCPT ); Mon, 9 Jan 2017 14:46:04 -0500 Date: Mon, 9 Jan 2017 14:46:00 -0500 From: Tejun Heo To: Shaohua Li Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, axboe@fb.com, vgoyal@redhat.com Subject: Re: [PATCH V5 05/17] blk-throttle: add upgrade logic for LIMIT_LOW state Message-ID: <20170109194600.GI12827@mtj.duckdns.org> References: <75685643afd126cbccefe894ca56fd5dd83fe8cf.1481833017.git.shli@fb.com> <20170109184053.GG12827@mtj.duckdns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170109184053.GG12827@mtj.duckdns.org> User-Agent: Mutt/1.7.1 (2016-10-04) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, again. On Mon, Jan 09, 2017 at 01:40:53PM -0500, Tejun Heo wrote: > I think it'd be great to explain the above. It was a bit difficult > for me to follow. It's also interesting because we're tying state > transitions for both read and write together. blk-throtl has been > handling reads and writes independently, now the mode switching from > low to max is shared across reads and writes. I suppose it could be > fine but would it be complex to separate them out? It's weird to make > this one state shared across reads and writes while not for others or > was this sharing intentional? I thought more about it and as the low limit is regulated by latency, it makes sense to make the state shared across reads and writes; otherwise, IOs in one direction could easily mess up the other direction. Can you please document that this is an intentional design and explain the rationale tho? Thanks. -- tejun