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

[Hans de Goede]

Hi,

On 06/27/2013 06:54 PM, Maxime Ripard wrote:
> On Thu, Jun 27, 2013 at 11:54:11AM +0200, Hans de Goede wrote:
> > 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).
>
> I searched a bit and it seems to be that discussion:
> https://groups.google.com/d/msg/linux-sunxi/gaTDngPT7Is/oeLtWb1N1wIJ
>
> > 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.
>
> Siarhei however notes that even higher-end SoCs like the exynos5 have
> similar performances with that regard. So I'm not sure we can do
> something about it, except what is suggested in the above mail, which
> looks rather unsafe.
>
> Anyway, like you said, we have no easy other solution, and we lacked
> such support until now.
>
> So why not merge this code for now, and try to optimise it later if we
> find it's needed.

That is fine with me, I just wanted to share that this has shown as
a bottleneck in some benchmarks in case anyone has a clever idea to
fix it ...

Regards,

Hans
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