Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752753AbaBPPju (ORCPT ); Sun, 16 Feb 2014 10:39:50 -0500 Received: from www.linutronix.de ([62.245.132.108]:49371 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751577AbaBPPjt (ORCPT ); Sun, 16 Feb 2014 10:39:49 -0500 Date: Sun, 16 Feb 2014 16:39:54 +0100 (CET) From: Thomas Gleixner To: Alexey Perevalov cc: John Stultz , linux-kernel@vger.kernel.org, anton@enomsg.org, kyungmin.park@samsung.com, akpm@linux-foundation.org, cw00.choi@samsung.com Subject: Re: [PATCH v2 0/3] Deferrable timers support for timerfd API In-Reply-To: <5300D752.5030403@samsung.com> Message-ID: References: <1389609835-24377-1-git-send-email-a.perevalov@samsung.com> <52DEC6A3.9020600@linaro.org> <52E606D8.6000401@samsung.com> <52F1DDA8.90605@samsung.com> <52F2B504.5010403@linaro.org> <52F3C8A5.708@samsung.com> <5300D752.5030403@samsung.com> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 16 Feb 2014, Alexey Perevalov wrote: > As I understand main idea in hrtimer.c was do not decrement expires_next in > case of DEFERRABLE timers type. > Such small average delay could be explained: it's due higher resolution, and > cpu is not in idle when we in hrtimer_interrupt, > with timer_list decrementing process not so often. > In this case it's hard to me to explain such small "time delta", it occurs > almost every time we have larger delay. Well, the point of deferrable timers is that they get executed, when the cpu is not idle, i.e. running some other timers as well I did not test my patch and I have no idea whether it really does what it should do, but tracing should tell you rather fast. So w/o instrumenting the kernel you can't tell why a timer is expired. Just looking at random numbers does not help. You need to create a proper test scenario which makes sure that the system goes into an extended nohz idle and then check whether the timers are deferred over that idle time. Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/