Re: [linux-sunxi] [PATCH 0/8] clocksource: sunxi: Timer fixes andcleanup

[Hans de Goede]

Hi,

On 06/27/2013 11:43 AM, Maxime Ripard wrote:
> On Thu, Jun 27, 2013 at 11:27:02AM +0200, Hans de Goede wrote:
> > Hi,
> >
> > On 06/26/2013 11:16 PM, Maxime Ripard wrote:
> > > Hi everyone,
> >
> > <snip>
> >
> > > It also finally adds a clocksource from the free running counter found in the
> > > A10/A13 SoCs.
> >
> > Hmm, have you benchmarked this? There have been reports from linux-sunxi kernel
> > users (xbmc project) that the waiting for the latch is quite slow. Note we
> > don't have anything better yet in the linux-sunxi kernel.
>
> No. I didn't.
>
> Do you have any pointers to these discussions?

The original discussion should be somewhere here:
https://groups.google.com/forum/#!forum/linux-sunxi

But I could not find it (it is probably hidden under
an unlogical subject).

Looking at my own notes (a small TODO file), I've
written down that the reporter reports:

 -current clocksource can cause us to run with interrupts disabled for 17%
  of the time, see "perf top" output

This is with a workload which does a lot of gettimeofday
calls.

I notice that unlike the sunxi-3.4 code you don't do any locking,
so how do you stop 2 clocksource calls from racing (and thus
getting a possible wrong value because of things not
being properly latched) ?

Regards,

Hans
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