From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:34800 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933800AbcKVXSk (ORCPT ); Tue, 22 Nov 2016 18:18:40 -0500 Date: Tue, 22 Nov 2016 15:18:24 -0800 From: Shaohua Li To: Tejun Heo CC: , , , , Subject: Re: [PATCH V4 07/15] blk-throttle: make throtl_slice tunable Message-ID: <20161122231824.GC14628@shli-mbp.local> References: <24137f881a149d30b98ef040367f26378128d4d2.1479161136.git.shli@fb.com> <20161122212715.GD17534@htj.duckdns.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" In-Reply-To: <20161122212715.GD17534@htj.duckdns.org> Sender: linux-block-owner@vger.kernel.org List-Id: linux-block@vger.kernel.org On Tue, Nov 22, 2016 at 04:27:15PM -0500, Tejun Heo wrote: > Hello, > > On Mon, Nov 14, 2016 at 02:22:14PM -0800, Shaohua Li wrote: > > throtl_slice is important for blk-throttling. A lot of stuffes depend on > > it, for example, throughput measurement. It has 100ms default value, > > which is not appropriate for all disks. For example, for SSD we might > > use a smaller value to make the throughput smoother. This patch makes it > > tunable. > > It bothers me a bit because time slice doesn't mean anything inherent > to throttling. It really is an implementation detail - throttling can > be implemented at per-operation level without time slice involved at > all. It's okay to expose the knob if necessary but the meaning of the > knob is almost completely arbitrary to users (as it has no inherent > meaning). Hmm, it's not a real 'time slice'. The name is a bit confusion. Maybe rename it to 'throtl_interval' or 'throtl_sampling_time'? not sure. bandwidth and iops are always in terms of a time interval we measure them. We can't say the iops/bw for a single io. So this is really a tuable knob. Thanks, Shaohua