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=-2.2 required=3.0 tests=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 61D4EC3A5A5 for ; Thu, 5 Sep 2019 09:06:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3E9042082E for ; Thu, 5 Sep 2019 09:06:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732964AbfIEJGf (ORCPT ); Thu, 5 Sep 2019 05:06:35 -0400 Received: from mx1.redhat.com ([209.132.183.28]:46610 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731737AbfIEJGf (ORCPT ); Thu, 5 Sep 2019 05:06:35 -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 80E5E8A1C9D; Thu, 5 Sep 2019 09:06:34 +0000 (UTC) Received: from ming.t460p (ovpn-8-16.pek2.redhat.com [10.72.8.16]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4053E5D9CA; Thu, 5 Sep 2019 09:06:23 +0000 (UTC) Date: Thu, 5 Sep 2019 17:06:19 +0800 From: Ming Lei To: Daniel Lezcano Cc: Bart Van Assche , Jens Axboe , Hannes Reinecke , Sagi Grimberg , linux-scsi@vger.kernel.org, Peter Zijlstra , Long Li , John Garry , LKML , linux-nvme@lists.infradead.org, Keith Busch , Ingo Molnar , Thomas Gleixner , Christoph Hellwig Subject: Re: [PATCH 1/4] softirq: implement IRQ flood detection mechanism Message-ID: <20190905090617.GB4432@ming.t460p> References: <20190828135054.GA23861@ming.t460p> <20190903033001.GB23861@ming.t460p> <299fb6b5-d414-2e71-1dd2-9d6e34ee1c79@linaro.org> <20190903063125.GA21022@ming.t460p> <6b88719c-782a-4a63-db9f-bf62734a7874@linaro.org> <20190903072848.GA22170@ming.t460p> <6f3b6557-1767-8c80-f786-1ea667179b39@acm.org> <2a8bd278-5384-d82f-c09b-4fce236d2d95@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2a8bd278-5384-d82f-c09b-4fce236d2d95@linaro.org> User-Agent: Mutt/1.11.3 (2019-02-01) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.69]); Thu, 05 Sep 2019 09:06:34 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 04, 2019 at 07:31:48PM +0200, Daniel Lezcano wrote: > Hi, > > On 04/09/2019 19:07, Bart Van Assche wrote: > > On 9/3/19 12:50 AM, Daniel Lezcano wrote: > >> On 03/09/2019 09:28, Ming Lei wrote: > >>> On Tue, Sep 03, 2019 at 08:40:35AM +0200, Daniel Lezcano wrote: > >>>> It is a scheduler problem then ? > >>> > >>> Scheduler can do nothing if the CPU is taken completely by handling > >>> interrupt & softirq, so seems not a scheduler problem, IMO. > >> > >> Why? If there is a irq pressure on one CPU reducing its capacity, the > >> scheduler will balance the tasks on another CPU, no? > > > > Only if CONFIG_IRQ_TIME_ACCOUNTING has been enabled. However, I don't > > know any Linux distro that enables that option. That's probably because > > that option introduces two rdtsc() calls in each interrupt. Given the > > overhead introduced by this option, I don't think this is the solution > > Ming is looking for. > > Was this overhead reported somewhere ? The syscall of gettimeofday() calls ktime_get_real_ts64() which finally calls tk_clock_read() which calls rdtsc too. But gettimeofday() is often used in fast path, and block IO_STAT needs to read it too. > > > See also irqtime_account_irq() in kernel/sched/cputime.c. > > From my POV, this framework could be interesting to detect this situation. Now we are talking about IRQ_TIME_ACCOUNTING instead of IRQ_TIMINGS, and the former one could be used to implement the detection. And the only sharing should be the read of timestamp. Thanks, Ming