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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 C5001C43441 for ; Mon, 12 Nov 2018 00:12:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 89A892084C for ; Mon, 12 Nov 2018 00:12:57 +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="sgJGCcsC" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 89A892084C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731182AbeKLKDX (ORCPT ); Mon, 12 Nov 2018 05:03:23 -0500 Received: from merlin.infradead.org ([205.233.59.134]:35084 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730559AbeKLKDW (ORCPT ); Mon, 12 Nov 2018 05:03:22 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.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:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=4PdzBjvYV7GribIfKWnTnyw2oELOvvEA5Bx4pMp6eCc=; b=sgJGCcsCYGo2fKYMms6AajQlU uD9vgz8TN9xsqJXaPhA0jgl11nhu5WdyY4XuwBwf35GBFslELOTbusRa1z6bPxI1DYCmpMCqBpQy5 yzJIVBtYocagLUIXlw1G/+GUXnwvOokq9TbgXJAoD1y6bUjZQWqYEoaqVECiRin51pxubJTW1eZEO haYOmsLg5agm7Dmu39YmWR1Mkoh7f0xQYNxfoufhMjbvFJ9V9I5auDoIjCsnr8qmdkWIr58IyK8cK pZFgRi/z+ntmWMhhVfyQiPd7WpmyvioRxd4orCXGpLKGLJDnR/7pVELLfbsMHC3kERe5ekVhKTFqw 21CIrcBrw==; Received: from [64.114.255.97] (helo=worktop) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1gLzqE-0004N7-Pm; Mon, 12 Nov 2018 00:12:34 +0000 Received: by worktop (Postfix, from userid 1000) id 6A1C46E061A; Mon, 12 Nov 2018 01:12:33 +0100 (CET) Date: Mon, 12 Nov 2018 01:12:33 +0100 From: Peter Zijlstra To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, Ingo Molnar Subject: Re: [PATCH tip/core/rcu 23/41] sched: Replace synchronize_sched() with synchronize_rcu() Message-ID: <20181112001233.GC3056@worktop> References: <20181111194104.GA4787@linux.ibm.com> <20181111194410.6368-23-paulmck@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181111194410.6368-23-paulmck@linux.ibm.com> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Nov 11, 2018 at 11:43:52AM -0800, Paul E. McKenney wrote: > Now that synchronize_rcu() waits for preempt-disable regions of code > as well as RCU read-side critical sections, synchronize_sched() can be > replaced by synchronize_rcu(). This commit therefore makes this change. Yes, but it also waits for an actual RCU quiestent state, which makes synchoinize_rcu() potentially much more expensive than an actual synchronize_sched(). So why are we doing this?