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Date: Wed, 9 Apr 2014 11:29:50 -0400 From: Steven Rostedt <rostedt@...dmis.org> To: Viresh Kumar <viresh.kumar@...aro.org> Cc: Thomas Gleixner <tglx@...utronix.de>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Matthew Whitehead <tedheadster@...il.com>, John Stultz <john.stultz@...aro.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, mwhitehe@...hat.com Subject: Re: nohz problem with idle time on old hardware On Wed, 9 Apr 2014 20:50:59 +0530 Viresh Kumar <viresh.kumar@...aro.org> wrote: > On 9 April 2014 20:01, Steven Rostedt <rostedt@...dmis.org> wrote: > > Ouch! You are correct, this part of the patch makes no sense. That's > > what I get for reviewing a patch and not looking at all the code around > > the changes. (another kernel developer hangs head in shame :-( ) > > > > I think that if statement should be nuked. > > Hmm, my opinion differs here :) > > If we completely remove this statement, we will run > tick_nohz_switch_to_nohz() even if nohz is not enabled. And check for > enabled must stay. Do we? This is only called by tick_check_oneshot_change() which has the following: int tick_check_oneshot_change(int allow_nohz) { struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched); if (!test_and_clear_bit(0, &ts->check_clocks)) return 0; if (ts->nohz_mode != NOHZ_MODE_INACTIVE) return 0; if (!timekeeping_valid_for_hres() || !tick_is_oneshot_available()) return 0; if (!allow_nohz) return 1; tick_nohz_switch_to_nohz(); return 0; } How often does it make it to that last check? -- Steve -- 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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