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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 EC3C1C282CE for ; Tue, 4 Jun 2019 18:21:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C2C00207E0 for ; Tue, 4 Jun 2019 18:21:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726638AbfFDSVa (ORCPT ); Tue, 4 Jun 2019 14:21:30 -0400 Received: from mx1.redhat.com ([209.132.183.28]:47722 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726179AbfFDSV3 (ORCPT ); Tue, 4 Jun 2019 14:21:29 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 31F5A30BC576; Tue, 4 Jun 2019 18:21:24 +0000 (UTC) Received: from llong.remote.csb (dhcp-17-85.bos.redhat.com [10.18.17.85]) by smtp.corp.redhat.com (Postfix) with ESMTP id 041AB5C207; Tue, 4 Jun 2019 18:21:21 +0000 (UTC) Subject: Re: [PATCH v8 15/19] locking/rwsem: Adaptive disabling of reader optimistic spinning To: Peter Zijlstra Cc: Ingo Molnar , Will Deacon , Thomas Gleixner , Borislav Petkov , "H. Peter Anvin" , linux-kernel@vger.kernel.org, x86@kernel.org, Davidlohr Bueso , Linus Torvalds , Tim Chen , huang ying References: <20190520205918.22251-1-longman@redhat.com> <20190520205918.22251-16-longman@redhat.com> <20190604092008.GJ3402@hirez.programming.kicks-ass.net> <8e7d19ea-f2e6-f441-6ab9-cbff6d96589c@redhat.com> <20190604173853.GG3419@hirez.programming.kicks-ass.net> <20190604181426.GH3419@hirez.programming.kicks-ass.net> From: Waiman Long Organization: Red Hat Message-ID: Date: Tue, 4 Jun 2019 14:21:21 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190604181426.GH3419@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.49]); Tue, 04 Jun 2019 18:21:29 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/4/19 2:14 PM, Peter Zijlstra wrote: >> I worked on this owner merging patch mainly to alleviate the need to use >> cmpxchg for reader lock. cmpxchg_double() is certainly one possible >> solution though it won't work on older CPUs. We can have a config option >> to use cmpxchg_double as it may increase the size of other structures >> that embedded rwsem and impose additional alignment constraint. > cmpxchg8b was introduced with the Pentium (for PAE IIRC, it enabled > atomic 64bit PTEs, but Linux never used it for that) and every Intel/AMD > thereafter has had it. AFAIK there's no x86_64 chip without cmpxchg16b. Thank for the clarification. I actually didn't check when cmpxch8b was introduced. I know it is a bit slower than regular cmpxchg. So we may still need to do some performance analysis to see how it compares with my current approach. Cheers, Longman