Re: schedule_timeout sleeps too long after dividing CPU frequency

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Thu, May 14, 2015 at 03:06:54PM +0200, Mason wrote:
> I added a printk inside twd_update_frequency().
> 
> http://lxr.free-electrons.com/source/arch/arm/kernel/smp_twd.c?v=3.14#L107
> 
> I inserted printk("NEW RATE=%lu\n", twd_timer_rate);
> right before the call to clockevents_update_freq().
> 
> When I execute "echo 18500 > scaling_max_freq"
> the system is supposed to change the CPU frequency to 18.5 MHz
> (I might have a bug lurking there) and PERIPHCLK is 1/2 of that,
> i.e 9.25 MHz.
> 
> twd_update_frequency() is called twice: once for each CPU.
> (The timers are local to each CPU.)

That's expected.

I wonder if clockevents_update_freq() is returning an error - which we
don't check, and don't print a warning.  It would probably be a very
good idea to print a warning as a failure to reconfigure the clock
events code for a different frequency will lead to this kind of issue.

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