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=-15.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 5F04AC433DB for ; Wed, 27 Jan 2021 23:26:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 18E4164DD0 for ; Wed, 27 Jan 2021 23:26:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235828AbhA0XZp (ORCPT ); Wed, 27 Jan 2021 18:25:45 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40804 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232351AbhA0W41 (ORCPT ); Wed, 27 Jan 2021 17:56:27 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 35DD9C06178C; Wed, 27 Jan 2021 14:37:44 -0800 (PST) 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=cvlrAJZnq6IX7KNiUIZWjYdQaLq5TVfCb9k0Y04B5QA=; b=mdyb7VqWn5FMZa/1xxFmi9xuhx XNFizrhQnqrgpWOKZGAF/GUyQ/IcM8+ejDoA4tWBkRuLFJSsF/MGr81LOuekbRSNQ6dHn9hererlK WtCxjnJthi1v/PmX52wi1lMxHuuMlJoggW7hfp4oYJgHQfELT4W2Cupzds5JqKAvdBn+HKDoXR/U2 X+Q6lQ+P7bwEJ4muUXonrRF62gx1thcujMZbIldCeHubMPpMgF7ksmw/hlJ/UQAFTZpPVyEQg/Jqx t0t+Z+7qTJ16LYMVOXnXbtvPbIMifaduR33PM5c5CyF49dNdndy+zY2X0bkVMrIGy8D5pUiNgGa6f 5WB3wihw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94 #2 (Red Hat Linux)) id 1l4tR9-007bYi-Vq; Wed, 27 Jan 2021 22:37:23 +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 AC7823010C8; Wed, 27 Jan 2021 23:37:19 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 990062BDDF79D; Wed, 27 Jan 2021 23:37:19 +0100 (CET) Date: Wed, 27 Jan 2021 23:37:19 +0100 From: Peter Zijlstra To: Alexander A Sverdlin Cc: Paul Burton , linux-mips@vger.kernel.org, Thomas Bogendoerfer , Will Deacon , Boqun Feng , Ingo Molnar , linux-kernel@vger.kernel.org Subject: Re: [PATCH 6/6] MIPS: cmpxchg: Use cmpxchg_local() for {cmp_}xchg_small() Message-ID: References: <20210127203627.47510-1-alexander.sverdlin@nokia.com> <20210127203627.47510-7-alexander.sverdlin@nokia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210127203627.47510-7-alexander.sverdlin@nokia.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 27, 2021 at 09:36:27PM +0100, Alexander A Sverdlin wrote: > From: Alexander Sverdlin > > It makes no sense to fold smp_mb__before_llsc()/smp_llsc_mb() again and > again, leave only one barrier pair in the outer function. > > This removes one SYNCW from __xchg_small() and brings around 10% > performance improvement in a tight spinlock loop with 6 threads on a 6 core > Octeon. > > Signed-off-by: Alexander Sverdlin > --- > arch/mips/kernel/cmpxchg.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/mips/kernel/cmpxchg.c b/arch/mips/kernel/cmpxchg.c > index 89107de..122e85f 100644 > --- a/arch/mips/kernel/cmpxchg.c > +++ b/arch/mips/kernel/cmpxchg.c > @@ -41,7 +41,7 @@ unsigned long __xchg_small(volatile void *ptr, unsigned long val, unsigned int s > do { > old32 = load32; > new32 = (load32 & ~mask) | (val << shift); > - load32 = cmpxchg(ptr32, old32, new32); > + load32 = cmpxchg_local(ptr32, old32, new32); > } while (load32 != old32); > > return (load32 & mask) >> shift; > @@ -97,7 +97,7 @@ unsigned long __cmpxchg_small(volatile void *ptr, unsigned long old, > */ > old32 = (load32 & ~mask) | (old << shift); > new32 = (load32 & ~mask) | (new << shift); > - load32 = cmpxchg(ptr32, old32, new32); > + load32 = cmpxchg_local(ptr32, old32, new32); > if (load32 == old32) > return old; > } This is wrong, please use cmpxchg_relaxed() which you've just introduced. cmpxchg_local() need not be cross-cpu atomic at all (it is on mips by accident of implementation).