I'm new to using this tool, but need to know if it will properly profile
each active CPU when the sampling interrupt is received. Currently, I'm
only using RTC sampling and the report shows nothing in regard to the used
CPUs. If NMI profiling were enabled for the P4 based platform, would the
results be any different?
From: John Levon <levon@mo...> - 2002-04-02 11:57:02
On Mon, Apr 01, 2002 at 01:50:43PM -0800, Ransford, Rusty wrote:
> I'm new to using this tool, but need to know if it will properly profile
> each active CPU when the sampling interrupt is received.
No, each interrupt causes only a local sampling. For RTC mode, this
relies on distribution of the RTC interrupt across the CPUs (so e.g.
noapic will mean only one CPU gets profiled).
For NMI mode, each CPU's counters + APIC is set up identically, so they
will each receive and handle their own LVTPC interrupts.
> only using RTC sampling and the report shows nothing in regard to the
> used CPUs.
I'm not sure what you would like reported ? Number of interrupts per CPU
? If you want to investigate this it's probably simplest to add a
printk() in module/oprofile.c:get_nr_interrupts()
In general the only cases where this would go wrong is badly distributed
RTC interrupts, so we haven't gone to the trouble of the necessary
sysctl details (instead just giving a global summary).
"That's just kitten-eating wrong."
- Richard Henderson
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