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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 9E412C76192 for ; Tue, 16 Jul 2019 11:04:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 643252173C for ; Tue, 16 Jul 2019 11:04:48 +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="kq39LOq6" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387513AbfGPLEr (ORCPT ); Tue, 16 Jul 2019 07:04:47 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:35026 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387421AbfGPLEr (ORCPT ); Tue, 16 Jul 2019 07:04:47 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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=V8XZvZAcUamsSZTab85Z64TRseHDkhL2kB2eADz4tBU=; b=kq39LOq6ikOI7FkK15EnJPIm2 GSYX7Nv6fUk6tyKjvX4zU26KYfvGHcwEDzdOS1KDha/TpjZy2UlhePyOmlSWnYhVU2El08XXvu8IH 9UTdM7DRYxtCU9EJLplTsaLAEC5QuqvzC2a1vYb4DpIJp6MpA2FVp2gC6P4Ky2GI492Th5FShcpJ0 vjdFbhoHVqM3Step7g08MgFwZFn9Ref1SYepQ2TdEFdmM1UF9Q/1Eq405Mox0ssaDaUOAf8lP0oqT fhBb5uLElUZ8gHTz833nqU8iHgg6PT9WvfJYGvD++u/Zhwe6XVi39WQeBF8epYRDVfv5+ZuknLnMp IzFBLXrHQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1hnLG1-0004dN-Ta; Tue, 16 Jul 2019 11:04:30 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 9DEA0201D171F; Tue, 16 Jul 2019 13:04:27 +0200 (CEST) Date: Tue, 16 Jul 2019 13:04:27 +0200 From: Peter Zijlstra To: Waiman Long Cc: Alex Kogan , linux@armlinux.org.uk, mingo@redhat.com, will.deacon@arm.com, arnd@arndb.de, 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, rahul.x.yadav@oracle.com Subject: Re: [PATCH v3 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock Message-ID: <20190716110427.GP3419@hirez.programming.kicks-ass.net> References: <20190715192536.104548-1-alex.kogan@oracle.com> <20190715192536.104548-4-alex.kogan@oracle.com> <77bba626-f3e6-45a8-aae8-43b945d0fab9@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <77bba626-f3e6-45a8-aae8-43b945d0fab9@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jul 15, 2019 at 05:30:01PM -0400, Waiman Long wrote: > On 7/15/19 3:25 PM, Alex Kogan wrote: > > /* > > - * On 64-bit architectures, the mcs_spinlock structure will be 16 bytes in > > - * size and four of them will fit nicely in one 64-byte cacheline. For > > - * pvqspinlock, however, we need more space for extra data. To accommodate > > - * that, we insert two more long words to pad it up to 32 bytes. IOW, only > > - * two of them can fit in a cacheline in this case. That is OK as it is rare > > - * to have more than 2 levels of slowpath nesting in actual use. We don't > > - * want to penalize pvqspinlocks to optimize for a rare case in native > > - * qspinlocks. > > + * On 64-bit architectures, the mcs_spinlock structure will be 20 bytes in > > + * size. For pvqspinlock or the NUMA-aware variant, however, we need more > > + * space for extra data. To accommodate that, we insert two more long words > > + * to pad it up to 36 bytes. > > */ > The 20 bytes figure is wrong. It is actually 24 bytes for 64-bit as the > mcs_spinlock structure is 8-byte aligned. For better cacheline > alignment, I will like to keep mcs_spinlock to 16 bytes as before. > Instead, you can use encode_tail() to store the CNA node pointer in > "locked". For instance, use (encode_tail() << 1) in locked to > distinguish it from the regular locked=1 value. Yes, please don't bloat this. I already don't like what Waiman did for the paravirt case, but this is horrible.