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Date: Wed, 22 Jan 2014 12:59:18 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Sasha Levin <sasha.levin@...cle.com> Cc: Arjan van de Ven <arjan@...ux.intel.com>, lenb@...nel.org, rjw@...ysocki.net, Eliezer Tamir <eliezer.tamir@...ux.intel.com>, rui.zhang@...el.com, jacob.jun.pan@...ux.intel.com, Mike Galbraith <bitbucket@...ine.de>, Ingo Molnar <mingo@...nel.org>, hpa@...or.com, paulmck@...ux.vnet.ibm.com, Thomas Gleixner <tglx@...utronix.de>, John Stultz <john.stultz@...aro.org>, Andy Lutomirski <luto@...capital.net>, linux-kernel@...r.kernel.org, dyoung@...hat.com Subject: Re: [PATCH 13/15] sched: Use a static_key for sched_clock_stable On Wed, Jan 22, 2014 at 11:45:32AM +0100, Peter Zijlstra wrote: > Ho humm. OK, so I had me a ponder; does the below fix things for you and David? I've only done a boot test on real proper hardware :-) --- kernel/sched/clock.c | 42 +++++++++++++++++++++++++++++++++--------- 1 file changed, 33 insertions(+), 9 deletions(-) diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c index 6bd6a6731b21..6bbcd97f4532 100644 --- a/kernel/sched/clock.c +++ b/kernel/sched/clock.c @@ -77,35 +77,45 @@ __read_mostly int sched_clock_running; #ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK static struct static_key __sched_clock_stable = STATIC_KEY_INIT; +static int __sched_clock_stable_early; int sched_clock_stable(void) { - if (static_key_false(&__sched_clock_stable)) - return false; - return true; + return static_key_false(&__sched_clock_stable); } void set_sched_clock_stable(void) { + __sched_clock_stable_early = 1; + + smp_mb(); /* matches sched_clock_init() */ + + if (!sched_clock_running) + return; + if (!sched_clock_stable()) - static_key_slow_dec(&__sched_clock_stable); + static_key_slow_inc(&__sched_clock_stable); } static void __clear_sched_clock_stable(struct work_struct *work) { /* XXX worry about clock continuity */ if (sched_clock_stable()) - static_key_slow_inc(&__sched_clock_stable); + static_key_slow_dec(&__sched_clock_stable); } static DECLARE_WORK(sched_clock_work, __clear_sched_clock_stable); void clear_sched_clock_stable(void) { - if (keventd_up()) - schedule_work(&sched_clock_work); - else - __clear_sched_clock_stable(&sched_clock_work); + __sched_clock_stable_early = 0; + + smp_mb(); /* matches sched_clock_init() */ + + if (!sched_clock_running) + return; + + schedule_work(&sched_clock_work); } struct sched_clock_data { @@ -140,6 +150,20 @@ void sched_clock_init(void) } sched_clock_running = 1; + + /* + * Ensure that it is impossible to not do a static_key update. + * + * Either {set,clear}_sched_clock_stable() must see sched_clock_running + * and do the update, or we must see their __sched_clock_stable_early + * and do the update, or both. + */ + smp_mb(); /* matches {set,clear}_sched_clock_stable() */ + + if (__sched_clock_stable_early) + set_sched_clock_stable(); + else + clear_sched_clock_stable(); } /* -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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