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,DKIM_INVALID, DKIM_SIGNED,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 0FBD2C433E3 for ; Mon, 13 Jul 2020 11:36:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E19E520738 for ; Mon, 13 Jul 2020 11:36:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Rrp2MoFa" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729646AbgGMLgS (ORCPT ); Mon, 13 Jul 2020 07:36:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57522 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726586AbgGMLgR (ORCPT ); Mon, 13 Jul 2020 07:36:17 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 633B4C061755; Mon, 13 Jul 2020 04:36:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; 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=e4mWSockMrHYbs1YPCBcxolKsfl3ywIczR6j7zoK7Fk=; b=Rrp2MoFaYyCYIte0PtkIcZ1FTZ MoSi4TD90kRTacj3VNqgEthpf25v6++DqVWCTLUCCUIJy2C2ZOLLLWsDjP+qLQn65OabUpDFB7Y9a w9dcH/7q9GE1V/blLC6eFCrYlsa5PaY5DZOPyBTTsUqVw+ck61Lmz3W3MeqQHHaBwu8PBde+s10EL BWS/EL8F/urrTrF/D2Rt6/2kkoOu4S7mhOtRV+wt3GdoWoP2caHZ0D4r1aB+0zBlSJprDCbtpMAxW bdbLccfPsJ1/yAvJqX45ca/K+gESVha4EHgJ8ZvEvxN2l0FZ6z+3rBQi9hSMHnm1WFHJl8n5F2F1L N47wrrSA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1juwkb-0003hh-Cg; Mon, 13 Jul 2020 11:36:01 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 865D0300F7A; Mon, 13 Jul 2020 13:36:00 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 6D38F20D28B50; Mon, 13 Jul 2020 13:36:00 +0200 (CEST) Date: Mon, 13 Jul 2020 13:36:00 +0200 From: peterz@infradead.org To: Qais Yousef Cc: Ingo Molnar , Doug Anderson , Jonathan Corbet , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Luis Chamberlain , Kees Cook , Iurii Zaikin , Quentin Perret , Valentin Schneider , Patrick Bellasi , Pavan Kondeti , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v6 1/2] sched/uclamp: Add a new sysctl to control RT default boost value Message-ID: <20200713113600.GA43129@hirez.programming.kicks-ass.net> References: <20200706142839.26629-1-qais.yousef@arm.com> <20200706142839.26629-2-qais.yousef@arm.com> <20200713112125.GG10769@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200713112125.GG10769@hirez.programming.kicks-ass.net> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 13, 2020 at 01:21:25PM +0200, Peter Zijlstra wrote: > + * copy_process() sysctl_uclamp > + * uclamp_min_rt = X; > + * write_lock(&tasklist_lock) read_lock(&tasklist_lock) > + * // link thread smp_mb__after_spinlock() > + * write_unlock(&tasklist_lock) read_unlock(&tasklist_lock); > + * sched_post_fork() for_each_process_thread() > + * __uclamp_sync_rt() __uclamp_sync_rt() > + * > + * Ensures that either sched_post_fork() will observe the new > + * uclamp_min_rt or for_each_process_thread() will observe the new > + * task. > + */ more specifically this has the cases: A) copy_process() sysctl_uclamp uclamp_min_rt = X; write_lock(&tasklist_lock) // link thread write_unlock(&tasklist_lock) sched_post_fork() read_lock(&tasklist_lock) __uclamp_sync_rt() smp_mb__after_spinlock() read_unlock(&tasklist_lock); for_each_process_thread() __uclamp_sync_rt() Where write_unlock()'s RELEASE matches read_lock() ACQUIRE and guarantees for_each_process_thread() must observe the new thread. B) copy_process() sysctl_uclamp uclamp_min_rt = X; read_lock(&tasklist_lock) smp_mb__after_spinlock() read_unlock(&tasklist_lock); write_lock(&tasklist_lock) for_each_process_thread() // link thread __uclamp_sync_rt() write_unlock(&tasklist_lock) sched_post_fork() __uclamp_sync_rt() Where read_unlock()'s RELEASE matches write_lock()'s ACQUIRE and sched_post_fork() must observe the uclamp_min_t STORE. The smp_mb__after_spinlock() might be superfluous, but like said, brain isn't working.