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=-5.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT 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 6ABA8C43381 for ; Mon, 1 Apr 2019 09:34:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3B971213A2 for ; Mon, 1 Apr 2019 09:34:11 +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="hXlpHWX9" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726534AbfDAJeK (ORCPT ); Mon, 1 Apr 2019 05:34:10 -0400 Received: from merlin.infradead.org ([205.233.59.134]:36952 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725832AbfDAJeJ (ORCPT ); Mon, 1 Apr 2019 05:34:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.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=AYMDSvhbnsbqhnhLpWaIkl1vWRlzxF1dhoJu98rOPYQ=; b=hXlpHWX9PJxQ6IOQGPiPGVNAo gWfhNZ1sXkF3fJYtFZdb++0l7NjjxN/zHMfBCBGW4TVwylzDdnx0nZBwM2Vi+wd+uadahNB8TC77X 0VoBa8SD5DbUmdPrqotODUib/5XBFtZDUHDV4Si0Q1+x5srdf+i94qOdhe5gwRtHMmZsbf7L7aQww G6yBNI+g6hBjIugEs77iN6OicnNwJQW/9p7jNNyEP6dYb5YoiPTjUP1RHKJPhAGZ+03BazMwBvPUe 5zoi3fYkK9kk+wxPFESEodyFdESJXXoGcTPTliMgNBHNbi/kHTXBHCRjmbncMCq8EhuAvPkZBBKIa 2aAQKyyNQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1hAtK8-0007w6-0u; Mon, 01 Apr 2019 09:33:48 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id B5E4C2026BE95; Mon, 1 Apr 2019 11:33:45 +0200 (CEST) Date: Mon, 1 Apr 2019 11:33:45 +0200 From: Peter Zijlstra To: Alex Kogan Cc: 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, steven.sistare@oracle.com, daniel.m.jordan@oracle.com, dave.dice@oracle.com, rahul.x.yadav@oracle.com Subject: Re: [PATCH v2 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock Message-ID: <20190401093345.GA14281@hirez.programming.kicks-ass.net> References: <20190329152006.110370-1-alex.kogan@oracle.com> <20190329152006.110370-4-alex.kogan@oracle.com> <20190401090653.GF11158@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190401090653.GF11158@hirez.programming.kicks-ass.net> 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, Apr 01, 2019 at 11:06:53AM +0200, Peter Zijlstra wrote: > On Fri, Mar 29, 2019 at 11:20:04AM -0400, Alex Kogan wrote: > > diff --git a/kernel/locking/mcs_spinlock.h b/kernel/locking/mcs_spinlock.h > > index bc6d3244e1af..71ee4b64c5d4 100644 > > --- a/kernel/locking/mcs_spinlock.h > > +++ b/kernel/locking/mcs_spinlock.h > > @@ -17,8 +17,18 @@ > > > > struct mcs_spinlock { > > struct mcs_spinlock *next; > > +#ifndef CONFIG_NUMA_AWARE_SPINLOCKS > > int locked; /* 1 if lock acquired */ > > int count; /* nesting count, see qspinlock.c */ > > +#else /* CONFIG_NUMA_AWARE_SPINLOCKS */ > > + uintptr_t locked; /* 1 if lock acquired, 0 if not, other values */ > > + /* represent a pointer to the secondary queue head */ > > + u32 node_and_count; /* node id on which this thread is running */ > > + /* with two lower bits reserved for nesting */ > > + /* count, see qspinlock.c */ > > + u32 encoded_tail; /* encoding of this node as the main queue tail */ > > + struct mcs_spinlock *tail; /* points to the secondary queue tail */ > > +#endif /* CONFIG_NUMA_AWARE_SPINLOCKS */ > > }; > > Please, have another look at the paravirt code, in particular at struct > pv_node and its usage. This is horrible. Thing is, this turns into a right mess when you also have PV spinlocks on. One thing we could maybe do is change locked and count to u8, then your overlay structure could be something like: struct mcs_spinlock { struct mcs_spinlock *next; u8 locked; u8 count; }; struct cna_node { /* struct mcs_spinlock overlay */ struct mcs_spinlock *next; u8 locked; u8 count; /* our CNA bits, consuming the slack and PV space */ u16 node; u32 encoded_tail; struct mcs_spinlock *head; struct mcs_spinlock *tail; }; Then you also don't need the first two patches.