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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 483F9C47082 for ; Tue, 8 Jun 2021 17:47:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2DBD6610E5 for ; Tue, 8 Jun 2021 17:47:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233898AbhFHRsy (ORCPT ); Tue, 8 Jun 2021 13:48:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47050 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233583AbhFHRsw (ORCPT ); Tue, 8 Jun 2021 13:48:52 -0400 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A7043C061574 for ; Tue, 8 Jun 2021 10:46:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=DYpoxF8V5padVKMwBrEXiIPopPnsff439+NPdx91qIw=; b=kCl98kyPH+JxVLSKJfvdpIWvAA GSj+ov9Kkbcj/ByFCmB/vpzwUt4Ah1e3MdHRj5u90yFFmj8i91AjqxMqGbnqnvMdw0vqqGYUUkXxL aygzPkEv6Muk4lW3ftlfgQkSm5M4tln2tJHZHR9FcW7j9pbwmo5eBixCtVV07+an6peYXrVUl0YG9 dW0f93RklivEdOE8qJYpA8z0K0Xip7T5fD5vjWP19Vi5DHB3WnEuBWnPqK0+10C7dhsK2g6HvXZxk pcbPF4FSkeUxX23IMnoDf7cQbKtZSf6NYJw4QHncFTeIDZ94YSgsSH2PwG8rdbiQ2da0KJ7TCGXl7 nR6CllLA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1lqfoN-004p8F-U9; Tue, 08 Jun 2021 17:46:54 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 4217B3001E3; Tue, 8 Jun 2021 19:46:54 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 1A2EF201E7EE3; Tue, 8 Jun 2021 19:46:54 +0200 (CEST) Date: Tue, 8 Jun 2021 19:46:54 +0200 From: Peter Zijlstra To: Beata Michalska Cc: Joel Fernandes , Valentin Schneider , Quentin Perret , LKML , Qais Yousef , Vincent Guittot , Viresh Kumar Subject: Re: iowait boost is broken Message-ID: References: <20210607191031.GA12489@e120325.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210607191031.GA12489@e120325.cambridge.arm.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.