Re: rtc mode vs. performance monitoring hardware mode

[John L. <le...@mo...>]

On Thu, Mar 14, 2002 at 10:46:56AM -0800, MONTGOMERY,BOB (HP-FtCollins,ex1) wrote:

> The rtc handler can never interrupt the NMI handler part of oprofile. The
> rtc handler can't profile any interesting interrupt handling code in the
> kernel.  The NMI handler could profile the rtc handler, but ... ?

Well exactly. At the least we'd need some check we're not in the rtc
handler. It complicates and slows down the most critical path in the
profiler ...

> Note that the rtc mode works badly on SMP systems.  Each interrupt is
> processed by only one of the CPUs in a sort of haphazard way (it seems).  I

This is dependent on your system (in particular using noapic will make
all interrupts go to CPU#0). The arbitration is supposed to distribute
interrupts evenly across the CPUs, and that's what I found happened in
my tests (well it's more complicated than that, but I  didn't see your
behaviour).

> up (it should still be on the same CPU that handled the RTC interrupt), it
> uses smp_call_function to run a pseudo-rtc handler function on the other

This is really like greasing a tortoise IMHO.

regards
john

-- 
I am a complete moron for forgetting about endianness. May I be
forever marked as such.