From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from esa5.hgst.iphmx.com ([216.71.153.144]:31796 "EHLO esa5.hgst.iphmx.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751737AbdDAXaF (ORCPT ); Sat, 1 Apr 2017 19:30:05 -0400 From: Bart Van Assche To: "linux-kernel@vger.kernel.org" , "osandov@osandov.com" , "linux-block@vger.kernel.org" , "axboe@fb.com" CC: "kernel-team@fb.com" Subject: Re: [PATCH] blk-mq: add random early detection I/O scheduler Date: Sat, 1 Apr 2017 23:29:55 +0000 Message-ID: <1491089381.9734.2.camel@sandisk.com> References: In-Reply-To: Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Sender: linux-block-owner@vger.kernel.org List-Id: linux-block@vger.kernel.org T24gU2F0LCAyMDE3LTA0LTAxIGF0IDE2OjA3IC0wNjAwLCBKZW5zIEF4Ym9lIHdyb3RlOg0KPiBP biAwNC8wMS8yMDE3IDAxOjU1IFBNLCBPbWFyIFNhbmRvdmFsIHdyb3RlOg0KPiA+IEZyb206IE9t YXIgU2FuZG92YWwgPG9zYW5kb3ZAZmIuY29tPg0KPiA+IA0KPiA+IFRoaXMgcGF0Y2ggaW50cm9k 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mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752057AbdDAXaI (ORCPT ); Sat, 1 Apr 2017 19:30:08 -0400 Received: from esa5.hgst.iphmx.com ([216.71.153.144]:31796 "EHLO esa5.hgst.iphmx.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751737AbdDAXaF (ORCPT ); Sat, 1 Apr 2017 19:30:05 -0400 X-IronPort-AV: E=Sophos;i="5.36,259,1486396800"; d="scan'208";a="7558152" Authentication-Results: spf=pass (sender IP is 74.221.232.54) smtp.mailfrom=sandisk.com; osandov.com; dkim=none (message not signed) header.d=none;osandov.com; dmarc=bestguesspass action=none header.from=sandisk.com; X-AuditID: ac1c2133-9afff7000000c960-1d-58e037f56189 From: Bart Van Assche To: "linux-kernel@vger.kernel.org" , "osandov@osandov.com" , "linux-block@vger.kernel.org" , "axboe@fb.com" CC: "kernel-team@fb.com" Subject: Re: [PATCH] blk-mq: add random early detection I/O scheduler Thread-Topic: [PATCH] blk-mq: add random early 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linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from base64 to 8bit by mail.home.local id v31NUIrk018613 On Sat, 2017-04-01 at 16:07 -0600, Jens Axboe wrote: > On 04/01/2017 01:55 PM, Omar Sandoval wrote: > > From: Omar Sandoval > > > > This patch introduces a new I/O scheduler based on the classic random > > early detection active queue management algorithm [1]. Random early > > detection is one of the simplest and most studied AQM algorithms for > > networking, but until now, it hasn't been applied to disk I/O > > scheduling. > > > > When applied to network routers, RED probabilistically either marks > > packets with ECN or drops them, depending on the configuration. When > > dealing with disk I/O, POSIX does not have any mechanism with which to > > notify the caller that the disk is congested, so we instead only provide > > the latter strategy. Included in this patch is a minor change to the > > blk-mq to support this. > > This is great work. If we combine this with a thin provisioning target, > we can even use this to save space on the backend. Better latencies, > AND lower disk utilization. > > I'm tempted to just queue this up for this cycle and make it the default. Hello Jens, Did you mean making this the default scheduler for SSDs only or for all types of block devices? Our (Western Digital) experience is that any I/O scheduler that limits the queue depth reduces throughput for at least data-center style workloads when using hard disks. This is why Adam is working on improving I/O priority support for the Linux block layer. That approach namely allows to reduce latency of certain requests without significantly impacting average latency and throughput. Bart.