Re: [BISECTED] "conservative" cpufreq governor broken

[Thomas Gleixner <tglx@linutronix.de>]

On Wed, 7 Oct 2009, Eero Nurkkala wrote:
> For some reason, this path is taken: 
> if (ts->nohz_mode == NOHZ_MODE_INACTIVE)
>         goto end;

Well, probably because the machine never switched to NOHZ :)
 
> > Also, this fix should probably be passed on to Greg K. H. (so it goes
> > in 2.6.31-stable) as well as Ingo Molnar (so it goes into -tip, and
> > hopefully to Linus for 2.6.32). Both CC'd.

Don't worry, it'll go the right way. No need to cc the world and some
more :)
 
> > - Steven
> 
> From: Eero Nurkkala <ext-eero.nurkkala@nokia.com>
> Date: Wed, 7 Oct 2009 11:54:26 +0300
> Subject: [PATCH] NOHZ: update idle state properly
> 
> Commit f2e21c9610991e95621a81407cdbab881226419b
> had unfortunate side effects with cpufreq governors on
> some systems.
> 
> If NOHZ_MODE_INACTIVE was set, ts->inidle was not being
> set. Then, all subsequent calls from irq_exit() bypassed
> calls to tick_nohz_start_idle() which resulted in wrong
> information passed to cpufreq governors. Fix this by
> updating the state of ts->inidle where it fits the best.

Hmm, nasty that code silently relies on NOHZ functionality even when
NOHZ is not active. That needs a big fat comment at least.

Nice detective work though !

Thanks,

	tglx