/proc/interrupts on unprivileged domains

/proc/interrupts on unprivileged domains

[Diwaker Gupta]

Hi everyone,

I'm trying to understand the values in /proc/interrupts of
unprivileged domains. Specifically, I'm interested in the value of the
timer interrupt. AFAIK, this value reflects the number of times this
domain received the timer interrupt from Xen? Equivalently, the number
of times the timer_interrupt() function (and thus the
do_timer_interrupt) function of the guest OS (linux, in this case)
were called? Please correct me if I'm wrong.

If that is indeed the case, then my real curiosity is this -- what
parameters affect this number? Again, AFAIK Xen gives a timer
interrupt periodically to a currently running domain, and also when a
domain gets scheduled. But how does this indirectly depend on other
parameters -- like the cpu frequency, the system time, the tsc
timestamp value and so on.

TIA
Diwaker

PS: I'm afraid I might not have been very articular in this email, but
I'm happy to give clarifications :)
-- 
Diwaker Gupta
http://resolute.ucsd.edu/diwaker


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Re: /proc/interrupts on unprivileged domains

[Keir Fraser]

> Hi everyone,
> 
> I'm trying to understand the values in /proc/interrupts of
> unprivileged domains. Specifically, I'm interested in the value of the
> timer interrupt. AFAIK, this value reflects the number of times this
> domain received the timer interrupt from Xen? Equivalently, the number
> of times the timer_interrupt() function (and thus the
> do_timer_interrupt) function of the guest OS (linux, in this case)
> were called? Please correct me if I'm wrong.

All correct.

> If that is indeed the case, then my real curiosity is this -- what
> parameters affect this number? Again, AFAIK Xen gives a timer
> interrupt periodically to a currently running domain, and also when a
> domain gets scheduled.

Xen gives a domain an interrupt every 10ms while it runs, and every
time the domain is rescheduled. It also gives an interrupt whenever
the domain's prgrammable one-shot timer expires (used by Linux to set
an appropriate  timeout whenever it blocks).

> But how does this indirectly depend on other
> parameters -- like the cpu frequency, the system time, the tsc
> timestamp value and so on.

It doesn't. :-)

 -- Keir


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