lkml.org 
[lkml]   [2014]   [May]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] ARM: Don't ever downscale loops_per_jiffy in SMP systems#
On Tue, May 13, 2014 at 07:29:52PM -0400, Nicolas Pitre wrote:
> On Tue, 13 May 2014, Nicolas Pitre wrote:
>
> > On Tue, 13 May 2014, Stephen Warren wrote:
> >
> > > On 05/13/2014 03:50 PM, Doug Anderson wrote:
> > > ...
> > > > ...but then I found the true problem shows up when we transition
> > > > between very low frequencies on exynos, like between 200MHz and
> > > > 300MHz. While transitioning between frequencies the system
> > > > temporarily bumps over to the "switcher" PLL running at 800MHz while
> > > > waiting for the main PLL to stabilize. No CPUFREQ notification is
> > > > sent for that. That means there's a period of time when we're running
> > > > at 800MHz but loops_per_jiffy is calibrated at between 200MHz and
> > > > 300MHz.
> > > >
> > > >
> > > > I'm welcome to any suggestions for how to address this. It sorta
> > > > feels like it would be a common thing to have a temporary PLL during
> > > > the transition, ...
> > >
> > > We definitely do that on Tegra for some cpufreq transitions.
> >
> > Ouch... If this is a common strategy to use a third frequency during a
> > transition phase, especially if that frequency is way off (800MHz vs
> > 200-300MHz) then it is something the cpufreq layer must capture and
> > advertise.
>
> Of course if only the loops_per_jiffy scaling does care about frequency
> changes these days, and if in those cases udelay() can instead be moved
> to a timer source on those hick-up prone platforms, then all this is
> fairly theoretical and may not be worth pursuing.

As I've been saying... use a bloody timer. :)

--
FTTC broadband for 0.8mile line: now at 9.7Mbps down 460kbps up... slowly
improving, and getting towards what was expected from it.


\
 
 \ /
  Last update: 2014-05-14 02:01    [W:0.087 / U:0.688 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site