Messages in this thread | | | Subject | Re: [PATCH] 2.6.17-rt add clockevent to ixp4xx | From | Milan Svoboda <> | Date | Fri, 14 Jul 2006 12:36:20 +0200 |
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Kevin,
> On Thu, 2006-07-13 at 10:53 +0000, Milan Svoboda wrote: > > > there are patches that enable clock event on ixp4xx platform. This should > > enable high resolution timers... Option for hrtimers in menuconfig is > > also enabled. > > Milan, > > I've also done a clockevent driver for ixp4xx and it looks pretty much > like yours. I've been waiting to submit as Thomas has recently reworked > the clockevent layer a bit in his -hrt-dyntick patchset. > > Here are a couple comments on your patchset > > - since you've registered the clockevent with CAP_TICK, both the > arch interrupt handler and the clockevent handler are handling the tick > and calling do_timer(). While I don't think this will negatively affect > timekeeping, it's unncessary overhead.
Yeah, I had a headache from this mistake, I found it a few minutes after sendig mail ;-)
> - why the addition of clockevent_hz2mult()? since shift is 32, you > could use existing div_sc32()
I didn't know about div_sc32... Simply, I have no problem with using div_sc32 now when I know that is exists ;-)
> The attached patch is a combination of my patch and yours and addresses > my comments above. I simply removed the CLOCK_CAP_TICK and removed your > clockevent_hz2mult() and used div_sc32(). >
Good.
> Also, below are a few runs of the nanosleep_jitter test that comes with > the sourceforge HRT test suite. Something strange is that with the > nanosleep_jitter test, I only see max sleeps of ~300-400 usec but with > your test I see max sleeps up to 1.3 msec. >
Maybe my test program is not as good as nanosleep_jitter :-)
I did patch against -hrt-dyntick (see lkml, this thread) wich is almost the same as this one against -rt (for ixp4xx part only) and I found that when timer is loaded with IXP4XX_OST_ONE_SHOT the latency time suddenly drops to ~30usec instead of ~2000usec! I'd like know what's the reason for this...
Best regards, Milan
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