From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E85F6C47094 for ; Thu, 10 Jun 2021 15:29:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CC166613C1 for ; Thu, 10 Jun 2021 15:29:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231644AbhFJPa7 (ORCPT ); Thu, 10 Jun 2021 11:30:59 -0400 Received: from foss.arm.com ([217.140.110.172]:34570 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231423AbhFJPa5 (ORCPT ); Thu, 10 Jun 2021 11:30:57 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 51706106F; Thu, 10 Jun 2021 08:29:01 -0700 (PDT) Received: from e107158-lin.cambridge.arm.com (e107158-lin.cambridge.arm.com [10.1.195.57]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3449F3F719; Thu, 10 Jun 2021 08:29:00 -0700 (PDT) Date: Thu, 10 Jun 2021 16:28:57 +0100 From: Qais Yousef To: Quentin Perret Cc: Peter Zijlstra , Beata Michalska , Joel Fernandes , Valentin Schneider , LKML , Vincent Guittot , Viresh Kumar Subject: Re: iowait boost is broken Message-ID: <20210610152857.lqtu2xl3364l6fyh@e107158-lin.cambridge.arm.com> References: <20210607191031.GA12489@e120325.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/09/21 09:50, Quentin Perret wrote: > On Tuesday 08 Jun 2021 at 19:46:54 (+0200), Peter Zijlstra wrote: > > On Mon, Jun 07, 2021 at 08:10:32PM +0100, Beata Michalska wrote: > > > So back to the expectations. > > > The main problem, as I see it, is what do we actually want to achieve with > > > the I/O boosting? Is it supposed to compensate the time lost while waiting > > > for the I/O request to be completed or is is supposed to optimize the rate > > > at which I/O requests are being made. > > > > The latter, you want to increase the race of submission. > > > > > Do we want to boost I/O bound tasks by > > > default, no limits applied or should we care about balancing performance > > > vs power ? And unless those expectations are clearly stated, we might not > > > get too far with any changes, really. > > > > You want to not increase power beyond what is needed to match the rate > > of processing I suppose. > > Note that in some cases we also don't care about throughput, and would > prefer to keep the frequency for some unimportant IO bound tasks (e.g. > background logging deamons and such). Uclamp.max indicates this to some > extent. In theory, one can have a user space daemon that monitors IO (via BPF?) and auto boost via uclamp. You can have allow/disallow list per-app too to setup the limits. So I say rm -rf iowait_boost and let's make it a user space problem :) /me runs -- Qais Yousef