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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 62A77C001DE for ; Fri, 4 Aug 2023 18:24:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229950AbjHDSYW (ORCPT ); Fri, 4 Aug 2023 14:24:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52952 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230452AbjHDSYS (ORCPT ); Fri, 4 Aug 2023 14:24:18 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 01D044C01; Fri, 4 Aug 2023 11:24:17 -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=0S9jBZoz5bVwPhGhUBlZgDmYofssuRkGRdTGWffFA4k=; b=DVWPLaFocHBV5YdbyIOimrmowF MqVimBeKhGRdAHpQGr3/dLOQeBvqub4KHNCFY4yXVywZzWyJ0yt8+IEhDsHnsSU3YuwEpt5Du8J/A g2GkkllBEBpJRWbnRwmg8RNa4AOGnFOSYkkDsTkte3XMeo/TXANopLvnpPu0Ks/PF3W5A1zJMlvog oahqJAzmJIXc9lXRVJDngbidVjZV412I8FzqP1yulLdcUSzCRvMnlDgJqw1R7m561SVm9cuuutGvy HkQS0bBdRhhj7PCQq8UVH1f5WXahPN+nPbpbM4i6MIxROtLGPienYbmWak8dY43B1SSHB8nNujUoL 8rQhHX0Q==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1qRzSD-00BMx5-JC; Fri, 04 Aug 2023 18:23:13 +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 (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id AB097300235; Fri, 4 Aug 2023 20:23:12 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 7F7EC21FA7B4A; Fri, 4 Aug 2023 20:23:12 +0200 (CEST) Date: Fri, 4 Aug 2023 20:23:12 +0200 From: Peter Zijlstra To: Guo Ren Cc: Alex Kogan , linux@armlinux.org.uk, mingo@redhat.com, will.deacon@arm.com, arnd@arndb.de, longman@redhat.com, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, bp@alien8.de, hpa@zytor.com, x86@kernel.org, guohanjun@huawei.com, jglauber@marvell.com, steven.sistare@oracle.com, daniel.m.jordan@oracle.com, dave.dice@oracle.com Subject: Re: [PATCH v15 3/6] locking/qspinlock: Introduce CNA into the slow path of qspinlock Message-ID: <20230804182312.GO212435@hirez.programming.kicks-ass.net> References: <20210514200743.3026725-1-alex.kogan@oracle.com> <20210514200743.3026725-4-alex.kogan@oracle.com> <20230803085004.GF212435@hirez.programming.kicks-ass.net> <20230803115610.GC214207@hirez.programming.kicks-ass.net> <20230804082531.GL212435@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Fri, Aug 04, 2023 at 10:17:35AM -0400, Guo Ren wrote: > > See, this is where the ARM64 WFE would come in handy; I don't suppose > > RISC-V has anything like that? > Em... arm64 smp_cond_load only could save power consumption or release > the pipeline resources of an SMT processor. When (Node1 cpu64) is in > the WFE state, it still needs (Node0 cpu1) to write the value to give > a cross-NUMA signal. So I didn't see what WFE related to reducing > cross-Numa transactions, or I missed something. Sorry The benefit is that WFE significantly reduces the memory traffic. Since it 'suspends' the core and waits for a write-notification instead of busy polling the memory location you get a ton less loads.