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=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 CFEE1C4360C for ; Tue, 8 Oct 2019 17:45:10 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 54C9A2070B for ; Tue, 8 Oct 2019 17:45:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 54C9A2070B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 46nl9b35pJzDqRb for ; Wed, 9 Oct 2019 04:45:07 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=softfail (mailfrom) smtp.mailfrom=linux.com (client-ip=3.19.106.255; helo=gentwo.org; envelope-from=cl@linux.com; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=linux.com Received: from gentwo.org (gentwo.org [3.19.106.255]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 46nl7Q1wk9zDqQT for ; Wed, 9 Oct 2019 04:43:13 +1100 (AEDT) Received: by gentwo.org (Postfix, from userid 1002) id 6438A3EC04; Tue, 8 Oct 2019 17:43:10 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by gentwo.org (Postfix) with ESMTP id 60AB53EC00; Tue, 8 Oct 2019 17:43:10 +0000 (UTC) Date: Tue, 8 Oct 2019 17:43:10 +0000 (UTC) From: Christopher Lameter X-X-Sender: cl@www.lameter.com To: Leonardo Bras Subject: Re: [PATCH v5 02/11] powerpc/mm: Adds counting method to monitor lockless pgtable walks In-Reply-To: <6e8877bff034603e75b35599797a39d9bc4840f1.camel@linux.ibm.com> Message-ID: References: <20191003013325.2614-1-leonardo@linux.ibm.com> <20191003013325.2614-3-leonardo@linux.ibm.com> <6e8877bff034603e75b35599797a39d9bc4840f1.camel@linux.ibm.com> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Song Liu , Michal Hocko , "Peter Zijlstra \(Intel\)" , Mahesh Salgaonkar , "Dmitry V. Levin" , Keith Busch , linux-mm@kvack.org, Paul Mackerras , Christian Brauner , Ira Weiny , Ingo Molnar , Elena Reshetova , linux-arch@vger.kernel.org, Santosh Sivaraj , Davidlohr Bueso , "Aneesh Kumar K.V" , Jann Horn , Mike Rapoport , Jason Gunthorpe , Allison Randal , Jesper Dangaard Brouer , Andrey Ryabinin , Alexey Dobriyan , Andrea Arcangeli , Ralph Campbell , Arnd Bergmann , Bartlomiej Zolnierkiewicz , John Hubbard , linuxppc-dev@lists.ozlabs.org, Nicholas Piggin , =?ISO-8859-15?Q?J=E9r=F4me_Glisse?= , Mathieu Desnoyers , kvm-ppc@vger.kernel.org, Dan Williams , Reza Arbab , Vlastimil Babka , Greg Kroah-Hartman , linux-kernel@vger.kernel.org, Thomas Gleixner , Souptick Joarder , Andrew Morton , Logan Gunthorpe , Roman Gushchin , "Kirill A. Shutemov" , Al Viro Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue, 8 Oct 2019, Leonardo Bras wrote: > > You are creating contention on a single exclusive cacheline. Doesnt this > > defeat the whole purpose of the lockless page table walk? Use mmap_sem or > > so should cause the same performance regression? > > Sorry, I did not understand that question. > I mean, this is just a refcount and never causes a lock. Locks also use atomic operations like a refcount increment. Both require the cacheline to be in exclusive state. So the impact is very similar.