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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 2C275C43143 for ; Tue, 2 Oct 2018 14:10:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EF62F2064A for ; Tue, 2 Oct 2018 14:10:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EF62F2064A Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729195AbeJBUyX convert rfc822-to-8bit (ORCPT ); Tue, 2 Oct 2018 16:54:23 -0400 Received: from mx1.redhat.com ([209.132.183.28]:37978 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727584AbeJBUyW (ORCPT ); Tue, 2 Oct 2018 16:54:22 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 1FBE23167697; Tue, 2 Oct 2018 14:10:49 +0000 (UTC) Received: from llong.remote.csb (dhcp-17-55.bos.redhat.com [10.18.17.55]) by smtp.corp.redhat.com (Postfix) with ESMTP id 7E58D5DD71; Tue, 2 Oct 2018 14:10:48 +0000 (UTC) Subject: Re: [PATCH 4/5] locking/lockdep: Make class->ops a percpu counter To: Ingo Molnar , Peter Zijlstra Cc: Ingo Molnar , Will Deacon , linux-kernel@vger.kernel.org References: <1538157201-29173-1-git-send-email-longman@redhat.com> <1538157201-29173-5-git-send-email-longman@redhat.com> <20181002093907.GV3439@hirez.programming.kicks-ass.net> <20181002095543.GA55344@gmail.com> From: Waiman Long Organization: Red Hat Message-ID: Date: Tue, 2 Oct 2018 10:10:48 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.0 MIME-Version: 1.0 In-Reply-To: <20181002095543.GA55344@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Tue, 02 Oct 2018 14:10:49 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/02/2018 05:55 AM, Ingo Molnar wrote: > * Peter Zijlstra wrote: > >> On Fri, Sep 28, 2018 at 01:53:20PM -0400, Waiman Long wrote: >>> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c >>> index ca002c0..7a0ed1d 100644 >>> --- a/kernel/locking/lockdep.c >>> +++ b/kernel/locking/lockdep.c >>> @@ -139,6 +139,7 @@ static inline int debug_locks_off_graph_unlock(void) >>> */ >>> unsigned long nr_lock_classes; >>> static struct lock_class lock_classes[MAX_LOCKDEP_KEYS]; >>> +static DEFINE_PER_CPU(unsigned long [MAX_LOCKDEP_KEYS], lock_class_ops); >>> @@ -1387,11 +1391,15 @@ static inline int usage_match(struct lock_list *entry, void *bit) >>> >>> static void print_lock_class_header(struct lock_class *class, int depth) >>> { >>> - int bit; >>> + int bit, cpu; >>> + unsigned long ops = 0UL; >>> + >>> + for_each_possible_cpu(cpu) >>> + ops += *per_cpu(class->pops, cpu); >>> >>> printk("%*s->", depth, ""); >>> print_lock_name(class); >>> - printk(KERN_CONT " ops: %lu", class->ops); >>> + printk(KERN_CONT " ops: %lu", ops); >>> printk(KERN_CONT " {\n"); >>> >>> for (bit = 0; bit < LOCK_USAGE_STATES; bit++) { >> That is an aweful lot of storage for a stupid number. Some archs >> (sparc64) are bzImage size constrained and this will hurt them. >> >> Ingo, do you happen to remember what that number was good for? > Just a spur of the moment statistics to satisfy curiousity, and it's useful to see how 'busy' a > particular class is, right? > >> Can't we simply ditch it? > We certainly could. Do we have roughly equivalent metrics to arrive at this number via other > methods? > > Thanks, > > Ingo One alternative is to group it under CONFIG_DEBUG_LOCKDEP again. This metric was originally under CONFIG_DEBUG_LOCKDEP, but was moved to CONFIG_LOCKDEP when trying to make other lock debugging statistics per-cpu counters. It was probably because this metric is per lock class while the rests are global. By doing so, you incur the memory cost only when CONFIG_DEBUG_LOCKDEP is defined. What do you think? Cheers, Longman