linux-kernel - Re: nohz and strange sleep latencies

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Date:	Sun, 25 Nov 2007 22:51:36 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Pavel Machek <pavel@....cz>, Ingo Molnar <mingo@...e.hu>,
	kernel list <linux-kernel@...r.kernel.org>
Subject: Re: nohz and strange sleep latencies

On Sun, 25 Nov 2007, Rafael J. Wysocki wrote:
> > Digging into process_32|64.c...
> > 
> > 64:
> >         while (1) {
> >                 while (!need_resched()) {
> >                         void (*idle)(void);
> > 
> >                         if (__get_cpu_var(cpu_idle_state))
> >                                 __get_cpu_var(cpu_idle_state) = 0;
> > 
> >                         tick_nohz_stop_sched_tick();
> > 
> > 32:
> >         while (1) {
> >                 tick_nohz_stop_sched_tick();
> >                 while (!need_resched()) {
> >                         void (*idle)(void);
> > 
> >                         if (__get_cpu_var(cpu_idle_state))
> >                                 __get_cpu_var(cpu_idle_state) = 0;
> > 
> > ...eek? Which one is wrong?
> 
> Hm, it looks like you should have quoted more lines ...
> 
> In the second case (32), the tick_nohz_stop_sched_tick() seems to be
> redundant, so I bet it's this one.

No. Both are fine. the 64bit version calls into
tick_nohz_stop_sched_tick() way to often. This is a leftover from the
old theory that we can have non-irq caused wakeups. Will fix it.

    tglx
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