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 9F94FC3A5A3 for ; Tue, 27 Aug 2019 23:05:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 80950214DA for ; Tue, 27 Aug 2019 23:05:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726340AbfH0XFL (ORCPT ); Tue, 27 Aug 2019 19:05:11 -0400 Received: from mx1.redhat.com ([209.132.183.28]:51492 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725992AbfH0XFL (ORCPT ); Tue, 27 Aug 2019 19:05:11 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 29CCF85365; Tue, 27 Aug 2019 23:05:11 +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 DD67560F82; Tue, 27 Aug 2019 23:04:57 +0000 (UTC) Date: Wed, 28 Aug 2019 07:04:52 +0800 From: Ming Lei To: Thomas Gleixner Cc: LKML , Long Li , Ingo Molnar , Peter Zijlstra , Keith Busch , Jens Axboe , Christoph Hellwig , Sagi Grimberg , John Garry , Hannes Reinecke , linux-nvme@lists.infradead.org, linux-scsi@vger.kernel.org, Daniel Lezcano Subject: Re: [PATCH 1/4] softirq: implement IRQ flood detection mechanism Message-ID: <20190827230451.GB5263@ming.t460p> References: <20190827085344.30799-1-ming.lei@redhat.com> <20190827085344.30799-2-ming.lei@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.3 (2019-02-01) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Tue, 27 Aug 2019 23:05:11 +0000 (UTC) Sender: linux-scsi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org On Tue, Aug 27, 2019 at 06:19:00PM +0200, Thomas Gleixner wrote: > On Tue, 27 Aug 2019, Thomas Gleixner wrote: > > On Tue, 27 Aug 2019, Ming Lei wrote: > > > +/* > > > + * Update average irq interval with the Exponential Weighted Moving > > > + * Average(EWMA) > > > + */ > > > +static void irq_update_interval(void) > > > +{ > > > +#define IRQ_INTERVAL_EWMA_WEIGHT 128 > > > +#define IRQ_INTERVAL_EWMA_PREV_FACTOR 127 > > > +#define IRQ_INTERVAL_EWMA_CURR_FACTOR (IRQ_INTERVAL_EWMA_WEIGHT - \ > > > + IRQ_INTERVAL_EWMA_PREV_FACTOR) > > > > Please do not stick defines into a function body. That's horrible. > > > > > + > > > + int cpu = raw_smp_processor_id(); > > > + struct irq_interval *inter = per_cpu_ptr(&avg_irq_interval, cpu); > > > + u64 delta = sched_clock_cpu(cpu) - inter->last_irq_end; > > > > Why are you doing that raw_smp_processor_id() dance? The call site has > > interrupts and preemption disabled. > > > > Also how is that supposed to work when sched_clock is jiffies based? > > > > > + inter->avg = (inter->avg * IRQ_INTERVAL_EWMA_PREV_FACTOR + > > > + delta * IRQ_INTERVAL_EWMA_CURR_FACTOR) / > > > + IRQ_INTERVAL_EWMA_WEIGHT; > > > > We definitely are not going to have a 64bit multiplication and division on > > every interrupt. Asided of that this breaks 32bit builds all over the place. > > That said, we already have infrastructure for something like this in the > core interrupt code which is optimized to be lightweight in the fast path. > > kernel/irq/timings.c irq/timings.c is much more complicated, especially it applies EWMA to compute each irq's average interval. However, we only need it for do_IRQ() to cover all interrupt & softirq handler. Also CONFIG_IRQ_TIMINGS is usually disabled on distributions. thanks, Ming