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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 7B21FC282CB for ; Fri, 8 Feb 2019 13:54:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 56B3520869 for ; Fri, 8 Feb 2019 13:54:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727767AbfBHNx7 (ORCPT ); Fri, 8 Feb 2019 08:53:59 -0500 Received: from Galois.linutronix.de ([146.0.238.70]:43867 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726641AbfBHNx7 (ORCPT ); Fri, 8 Feb 2019 08:53:59 -0500 Received: from localhost ([127.0.0.1] helo=nanos.tec.linutronix.de) by Galois.linutronix.de with esmtp (Exim 4.80) (envelope-from ) id 1gs6bK-000296-Sh; Fri, 08 Feb 2019 14:53:55 +0100 Message-Id: <20190208135021.013828701@linutronix.de> User-Agent: quilt/0.65 Date: Fri, 08 Feb 2019 14:48:04 +0100 From: Thomas Gleixner To: LKML Cc: Waiman Long , Matthew Wilcox , Andrew Morton , Alexey Dobriyan , Kees Cook , linux-fsdevel@vger.kernel.org, Davidlohr Bueso , Miklos Szeredi , Daniel Colascione , Dave Chinner , Randy Dunlap , Marc Zyngier Subject: [patch V2 2/2] proc/stat: Make the interrupt statistics more efficient References: <20190208134802.218483159@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Waiman reported that on large systems with a large amount of interrupts the readout of /proc/stat takes a long time to sum up the interrupt statistics. In principle this is not a problem. but for unknown reasons some enterprise quality software reads /proc/stat with a high frequency. The reason for this is that interrupt statistics are accounted per cpu. So the /proc/stat logic has to sum up the interrupt stats for each interrupt. The interrupt core provides now a per interrupt summary counter which can be used to avoid the summation loops completely except for interrupts marked PER_CPU which are only a small fraction of the interrupt space if at all. Another simplification is to iterate only over the active interrupts and skip the potentially large gaps in the interrupt number space and just print zeros for the gaps without going into the interrupt core in the first place. Waiman provided test results from a 4-socket IvyBridge-EX system (60-core 120-thread, 3016 irqs) excuting a test program which reads /proc/stat 50,000 times: Before: 18.436s (sys 18.380s) After: 3.769s (sys 3.742s) Reported-by: Waiman Long Signed-off-by: Thomas Gleixner --- v2: Make variables unsigned int. Add results to changelog. fs/proc/stat.c | 29 ++++++++++++++++++++++++++--- 1 file changed, 26 insertions(+), 3 deletions(-) --- a/fs/proc/stat.c +++ b/fs/proc/stat.c @@ -79,6 +79,31 @@ static u64 get_iowait_time(int cpu) #endif +static void show_irq_gap(struct seq_file *p, unsigned int gap) +{ + static const char zeros[] = " 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0"; + + while (gap > 0) { + unsigned int inc; + + inc = min_t(unsigned int, gap, ARRAY_SIZE(zeros) / 2); + seq_write(p, zeros, 2 * inc); + gap -= inc; + } +} + +static void show_all_irqs(struct seq_file *p) +{ + unsigned int i, next = 0; + + for_each_active_irq(i) { + show_irq_gap(p, i - next); + seq_put_decimal_ull(p, " ", kstat_irqs_usr(i)); + next = i + 1; + } + show_irq_gap(p, nr_irqs - next); +} + static int show_stat(struct seq_file *p, void *v) { int i, j; @@ -156,9 +181,7 @@ static int show_stat(struct seq_file *p, } seq_put_decimal_ull(p, "intr ", (unsigned long long)sum); - /* sum again ? it could be updated? */ - for_each_irq_nr(j) - seq_put_decimal_ull(p, " ", kstat_irqs_usr(j)); + show_all_irqs(p); seq_printf(p, "\nctxt %llu\n"