Re: A clocksource question

[Jeremy Fitzhardinge <jeremy@goop.org>]

On 03/11/2010 04:27 PM, Joanna Rutkowska wrote:
> I think that the important clue is this message appearing in my dmesg
> (in Dom0 and also in DomUs):
>
> hrtimer: interrupt too slow, forcing clock min delta to 540150561 ns
>
> This is almost 0.5s (!) and I think this might explain my kbd hiccup. I
> wrote that I feel it every 10s or so, but when I was playing on my
> system without jiffies setting today, I saw this hiccup occurring much
> more often; in fact it was more of a "slow keyboard/system" feeling than
> a hiccup".
>    

Yes, its definitely a good clue.  It could point to a Xen scheduler 
issue (I assume you don't have any other busy domains when this is going 
on), but that wouldn't explain why it works OK with jiffies.  Perhaps 
there's a problem with programming the timer so that sometimes it gets 
missed and the system doesn't get a kick until some subsequent event 
(whereas with clocksource=jiffies there'll always be a timer in the next 
100ms).

     J