Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751631AbdGaUUr (ORCPT ); Mon, 31 Jul 2017 16:20:47 -0400 Received: from mail-lf0-f48.google.com ([209.85.215.48]:36183 "EHLO mail-lf0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751052AbdGaUUq (ORCPT ); Mon, 31 Jul 2017 16:20:46 -0400 From: Marcin Wojtas To: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Cc: catalin.marinas@arm.com, will.deacon@arm.com, andrew@lunn.ch, thomas.petazzoni@free-electrons.com, gregory.clement@free-electrons.com, nadavh@marvell.com, neta@marvell.com, mw@semihalf.com, jaz@semihalf.com, tn@semihalf.com Subject: [PATCH] arm64: defconfig: enable fine-grained task level IRQ time accounting Date: Mon, 31 Jul 2017 22:22:11 +0200 Message-Id: <1501532531-4499-1-git-send-email-mw@semihalf.com> X-Mailer: git-send-email 1.8.3.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2289 Lines: 53 Tests showed, that under certain conditions, the summary number of jiffies spent on softirq/idle, which are counted by system statistics can be even below 10% of expected value, resulting in false load presentation. The issue was observed on the quad-core Marvell Armada 8k SoC, whose two 10G ports were bound into L2 bridge. Load was controlled by bidirectional UDP traffic, produced by a packet generator. Under such condition, the dominant load is softirq. With 100% single CPU occupation or without any activity (all CPUs 100% idle), total number of jiffies is 10000 (2500 per each core) in 10s interval. Also with other kind of load this was true. However below a saturation threshold it was observed, that with CPU which was occupied almost by softirqs only, the statistic were awkward. See the mpstat output: CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle all 0.00 0.00 0.13 0.00 0.00 0.55 0.00 0.00 0.00 99.32 0 0.00 0.00 0.00 0.00 0.00 23.08 0.00 0.00 0.00 76.92 1 0.00 0.00 0.40 0.00 0.00 0.00 0.00 0.00 0.00 99.60 2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00 Above would mean basically no total load, debug CPU0 occupied in 25%. Raw statistics, printed every 10s from /proc/stat unveiled a root cause - summary idle/softirq jiffies on loaded CPU were below 200, i.e. over 90% samples lost. All problems were gone after enabling fine granulity IRQ time accounting. This patch fixes possible wrong statistics processing by enabling CONFIG_IRQ_TIME_ACCOUNTING for arm64 platfroms, which is by default done on other architectures, e.g. x86 and arm. Tests showed no noticeable performance penalty, nor stability impact. Signed-off-by: Marcin Wojtas --- arch/arm64/configs/defconfig | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/arm64/configs/defconfig b/arch/arm64/configs/defconfig index 44423e6..ed51ac6 100644 --- a/arch/arm64/configs/defconfig +++ b/arch/arm64/configs/defconfig @@ -3,6 +3,7 @@ CONFIG_POSIX_MQUEUE=y CONFIG_AUDIT=y CONFIG_NO_HZ_IDLE=y CONFIG_HIGH_RES_TIMERS=y +CONFIG_IRQ_TIME_ACCOUNTING=y CONFIG_BSD_PROCESS_ACCT=y CONFIG_BSD_PROCESS_ACCT_V3=y CONFIG_TASKSTATS=y -- 1.8.3.1