Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755937AbaAFShc (ORCPT ); Mon, 6 Jan 2014 13:37:32 -0500 Received: from mail-pb0-f53.google.com ([209.85.160.53]:56844 "EHLO mail-pb0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755235AbaAFShb (ORCPT ); Mon, 6 Jan 2014 13:37:31 -0500 From: Kevin Hilman To: Frederic Weisbecker Cc: Thomas Gleixner , linux-kernel@vger.kernel.org, linaro-kernel@lists.linaro.org, Ingo Molnar , Peter Zijlstra Subject: Re: [PATCH 1/2] sched/nohz: add debugfs control over sched_tick_max_deferment References: <1387315388-31676-1-git-send-email-khilman@linaro.org> <20140105132153.GA25212@localhost.localdomain> Date: Mon, 06 Jan 2014 10:37:27 -0800 In-Reply-To: <20140105132153.GA25212@localhost.localdomain> (Frederic Weisbecker's message of "Sun, 5 Jan 2014 14:21:55 +0100") Message-ID: <87eh4lez2w.fsf@linaro.org> User-Agent: Gnus/5.130008 (Ma Gnus v0.8) Emacs/24.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Frederic Weisbecker writes: > On Tue, Dec 17, 2013 at 01:23:07PM -0800, Kevin Hilman wrote: >> Allow debugfs override of sched_tick_max_deferment in order to ease >> finding/fixing the remaining issues with full nohz. >> >> The value to be written is in jiffies, and -1 means the max deferment >> is disabled (scheduler_tick_max_deferment() returns KTIME_MAX.) >> >> Cc: Frederic Weisbecker >> Signed-off-by: Kevin Hilman >> --- >> kernel/sched/core.c | 16 +++++++++++++++- >> 1 file changed, 15 insertions(+), 1 deletion(-) >> >> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >> index 5ac63c9a995a..4b1fe3e69fe4 100644 >> --- a/kernel/sched/core.c >> +++ b/kernel/sched/core.c >> @@ -2175,6 +2175,8 @@ void scheduler_tick(void) >> } >> >> #ifdef CONFIG_NO_HZ_FULL >> +static u32 sched_tick_max_deferment = HZ; >> + >> /** >> * scheduler_tick_max_deferment >> * >> @@ -2193,13 +2195,25 @@ u64 scheduler_tick_max_deferment(void) >> struct rq *rq = this_rq(); >> unsigned long next, now = ACCESS_ONCE(jiffies); >> >> - next = rq->last_sched_tick + HZ; >> + if (sched_tick_max_deferment == -1) >> + return KTIME_MAX; >> + >> + next = rq->last_sched_tick + sched_tick_max_deferment; >> >> if (time_before_eq(next, now)) >> return 0; >> >> return jiffies_to_usecs(next - now) * NSEC_PER_USEC; >> } >> + >> +static __init int sched_nohz_full_init_debug(void) >> +{ >> + debugfs_create_u32("sched_tick_max_deferment", 0644, NULL, >> + &sched_tick_max_deferment); >> + >> + return 0; >> +} >> +late_initcall(sched_nohz_full_init_debug); > > If the goal is mostly to turn off sched_tick_max_deferment (set to -1), we should > perhaps make it a boolean sched feature (see kernel/sched/features.h) as it's a pretty > well consolidated interface. Well, I suspect folks may want to set it to various values, depending on workload to experiment with the results. Also, my first attempt was to add control over this via sysctl[1] (though not sched_features) and you suggested[2] I use debugfs instead since this should be a temporary hack until we can remove the 1Hz residual tick. Kevin [1] http://marc.info/?l=linux-kernel&m=137159992306877&w=2 [2] http://marc.info/?l=linux-kernel&m=137166737830821&w=2 -- 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/