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[73.231.122.98]) by smtp.googlemail.com with ESMTPSA id x13sm39205922pfa.72.2016.02.29.08.22.55 (version=TLSv1/SSLv3 cipher=OTHER); Mon, 29 Feb 2016 08:22:56 -0800 (PST) Message-ID: <1456762914.648.76.camel@edumazet-ThinkPad-T530> Subject: Re: Softirq priority inversion from "softirq: reduce latencies" From: Eric Dumazet To: Peter Hurley Cc: Mike Galbraith , Francois Romieu , Eric Dumazet , David Miller , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Greg KH , dmaengine@vger.kernel.org, John Ogness , Sebastian Andrzej Siewior , Andrew Morton , Thomas Gleixner Date: Mon, 29 Feb 2016 08:21:54 -0800 In-Reply-To: <56D469B2.2070707@hurleysoftware.com> References: <56D1E8B6.6090003@hurleysoftware.com> <1456638957.3676.12.camel@gmail.com> <20160228170109.GA16322@electric-eye.fr.zoreil.com> <1456721889.3488.67.camel@gmail.com> <56D45DAF.5070709@hurleysoftware.com> <1456759153.648.61.camel@edumazet-ThinkPad-T530> <56D469B2.2070707@hurleysoftware.com> X-Mailer: Evolution 3.10.4-0ubuntu2 Mime-Version: 1.0 Sender: dmaengine-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: dmaengine@vger.kernel.org X-Spam-Status: No, score=-6.8 required=5.0 tests=BAYES_00, DKIM_ADSP_CUSTOM_MED, DKIM_SIGNED, FREEMAIL_FROM, RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD, T_DKIM_INVALID, UNPARSEABLE_RELAY autolearn=ham version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP On lun., 2016-02-29 at 07:54 -0800, Peter Hurley wrote: > The current kernel is HZ=250 but this would occur on HZ=1000 as well. Right. But the problem with HZ=100 and HZ=250 is that the detection can happens because jiffy granularity is too coarse, since msecs_to_jiffies(2) -> 1 Following patch might reduce the probability, but wont really fix your problem. Fact that ksoftirqd prio is not what you want is completely orthogonal. --- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html diff --git a/kernel/softirq.c b/kernel/softirq.c index 479e443..f7cc594 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -180,7 +180,7 @@ EXPORT_SYMBOL(__local_bh_enable_ip); /* * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times, - * but break the loop if need_resched() is set or after 2 ms. + * but break the loop if need_resched() is set or after 2 ms/ticks. * The MAX_SOFTIRQ_TIME provides a nice upper bound in most cases, but in * certain cases, such as stop_machine(), jiffies may cease to * increment and so we need the MAX_SOFTIRQ_RESTART limit as @@ -191,7 +191,7 @@ EXPORT_SYMBOL(__local_bh_enable_ip); * we want to handle softirqs as soon as possible, but they * should not be able to lock up the box. */ -#define MAX_SOFTIRQ_TIME msecs_to_jiffies(2) +#define MAX_SOFTIRQ_TIME (1 + msecs_to_jiffies(2)) #define MAX_SOFTIRQ_RESTART 10 #ifdef CONFIG_TRACE_IRQFLAGS