linux-kernel - Re: [PATCH v7 2/4] cpufreq: ondemand: call dbs_check

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Date:	Wed, 30 Jan 2013 22:41:08 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	Fabio Baltieri <fabio.baltieri@...aro.org>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, cpufreq@...r.kernel.org,
	linux-pm@...r.kernel.org, Linus Walleij <linus.walleij@...aro.org>,
	swarren@...dotorg.org, linaro-dev@...ts.linaro.org,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	mathieu.poirier@...aro.org, Joseph Lo <josephl@...dia.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 2/4] cpufreq: ondemand: call dbs_check_cpu only when necessary

On 30 January 2013 22:16, Fabio Baltieri <fabio.baltieri@...aro.org> wrote:
> Isn't that how it works now?  The current cpu ktime is not checked
> against its own, but against the "leader" cpu (dbs_info_local->cdbs.cpu),
> that's why it's initialized only for the first.
>
> Maybe I should have used dbs_info_leader/dbs_info instead of
> dbs_info_local/dbs_info.

This routine is called as wq handler. Which will recover dbs_info from work
using container_of. Which would give dbs_info_local for the cpu j.

Then we will execute below code.

+       /* use leader CPU's dbs_info */
+       dbs_info = &per_cpu(od_cpu_dbs_info, dbs_info_local->cdbs.cpu);

dbs_info_local->cdbs.cpu was uninitialized for all cpus except policy->cpu.
And so, might be initialized with 0 as its a global variable... But if you
offline cpu 0 and online it back, then policy->cpu would be 1 and this logic,
which worked by mistake will fail.

+       mutex_lock(&dbs_info->cdbs.timer_mutex);
+
+       time_now = ktime_get();
+       delta_us = ktime_us_delta(time_now, dbs_info->cdbs.time_stamp);

and so as this.

Correct?
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