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 4C576C2D0CE for ; Tue, 21 Jan 2020 13:31:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1E56B217F4 for ; Tue, 21 Jan 2020 13:31:05 +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="wumgBDv6" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728898AbgAUNbE (ORCPT ); Tue, 21 Jan 2020 08:31:04 -0500 Received: from merlin.infradead.org ([205.233.59.134]:43374 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725890AbgAUNbE (ORCPT ); Tue, 21 Jan 2020 08:31:04 -0500 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=sQsNUT1I6E8QItPKtSDNxr8kzUBb8jOWCVawdbMbuhs=; b=wumgBDv6cNBhEJASXpiGDNAAA fIjFViuZ/mfovC47v2shUCqKUf1OHOHGHCqlPOvQ1A7JID+0E02moRI0efYbudsqlBXR/o+B+mGN5 mxIMenqLi4lcXgHyX6fCzBEzOsMdRXvfiIht1UCcGvWIe/7idW3F02/5yuTujrnLupRkFDzhwre64 0e3Tb0KiaEV35OILtmALggkTSogvX2c4NUq6SAxjY4o624HXSoftOhLihn9/jnyMmejE86xuOmlNz d4dQ2iYkRLOzMPuMT9CR6NFW2DiezhfzlklTPofyQ86qCl400zrucJA1Mux8uWyHG3//ShnZLO7TL y5ils314w==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1ittbO-0006Ql-0z; Tue, 21 Jan 2020 13:29:54 +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 B9A1F3043C9; Tue, 21 Jan 2020 14:28:10 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id D89C520983FD9; Tue, 21 Jan 2020 14:29:49 +0100 (CET) Date: Tue, 21 Jan 2020 14:29:49 +0100 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, guohanjun@huawei.com, jglauber@marvell.com, steven.sistare@oracle.com, daniel.m.jordan@oracle.com, dave.dice@oracle.com Subject: Re: [PATCH v8 4/5] locking/qspinlock: Introduce starvation avoidance into CNA Message-ID: <20200121132949.GL14914@hirez.programming.kicks-ass.net> References: <20191230194042.67789-1-alex.kogan@oracle.com> <20191230194042.67789-5-alex.kogan@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191230194042.67789-5-alex.kogan@oracle.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, Dec 30, 2019 at 02:40:41PM -0500, Alex Kogan wrote: > +/* > + * Controls the threshold for the number of intra-node lock hand-offs before > + * the NUMA-aware variant of spinlock is forced to be passed to a thread on > + * another NUMA node. By default, the chosen value provides reasonable > + * long-term fairness without sacrificing performance compared to a lock > + * that does not have any fairness guarantees. The default setting can > + * be changed with the "numa_spinlock_threshold" boot option. > + */ > +int intra_node_handoff_threshold __ro_after_init = 1 << 16; There is a distinct lack of quantitative data to back up that 'reasonable' claim there. Where is the table of inter-node latencies observed for the various values tested, and on what criteria is this number deemed reasonable? To me, 64k lock hold times seems like a giant number, entirely outside of reasonable. > + > static void __init cna_init_nodes_per_cpu(unsigned int cpu) > { > struct mcs_spinlock *base = per_cpu_ptr(&qnodes[0].mcs, cpu); > @@ -97,6 +109,11 @@ static int __init cna_init_nodes(void) > } > early_initcall(cna_init_nodes); > > +static __always_inline void cna_init_node(struct mcs_spinlock *node) > +{ > + ((struct cna_node *)node)->intra_count = 0; > +} > + > /* this function is called only when the primary queue is empty */ > static inline bool cna_try_change_tail(struct qspinlock *lock, u32 val, > struct mcs_spinlock *node) > @@ -233,7 +250,9 @@ __always_inline u32 cna_pre_scan(struct qspinlock *lock, > { > struct cna_node *cn = (struct cna_node *)node; > > - cn->pre_scan_result = cna_scan_main_queue(node, node); > + cn->pre_scan_result = > + cn->intra_count == intra_node_handoff_threshold ? > + FLUSH_SECONDARY_QUEUE : cna_scan_main_queue(node, node); Because: if (cn->intra_count < intra_node_handoff_threshold) cn->pre_scan_result = cna_scan_main_queue(node, node); else cn->pre_scan_result = FLUSH_SECONDARY_QUEUE; was too readable?