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Re: [Xen-devel] [PATCH] remove blocked time accounting from xen "clockchip"



On 10/19/11 09:51, Jan Beulich wrote:
On 18.10.11 at 22:42, Laszlo Ersek<lersek@xxxxxxxxxx>  wrote:
... because the "clock_event_device framework" already accounts for idle
time through the "event_handler" function pointer in
xen_timer_interrupt().

As event_handler is being checked to be non-zero, shouldn't the
code you remove simply become conditional (upon event_handler
being zero)?

I think that wouldn't be hard to implement, but I'm afraid the paragraph you quoted from my proposed commit message could be wrong -- perhaps it's not the event_handler callback that cranks the idle time counter. Please see

https://bugzilla.redhat.com/show_bug.cgi?id=624756#c26

In short,

(a) idle time is increased in cpu_idle(), which seems to be running as a standalone kernel thread;

(b) the event_handler I found invoked from xen_timer_interrupt() is hrtimer_interrupt();

(c) I couldn't figure out if cpu_idle() keeps waking up "on its own", or if it needs periodic kicks from hrtimer_interrupt() (executed by some other thread).

Thank you
Laszlo

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