perfctr-2.7.3 for 2.6.7-rc1-mm1: core
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[few points I just noticed]
Quoted 3 lines · Andrew Morton
- a general overview of how the whole thing operates (what's
PERFCTR_INTERRUPT_SUPPORTdo? What interrupts are generated? Describe
The hardware can usually generate an interrupt when the performance counter under or overflows. oprofile uses this too.
Quoted 1 line
the backpatching design, etc). What is "forbidden" on p4 siblings, and
p4 siblings share only a single set of performance counters, so you must keep them synchronized.
Quoted 3 lines
- <canofworms>cannot
cpus_copy_to_user()share code with sys_sched_getaffinity()?</canofworms>
The sched_getaffinity code for that is broken, I'm about to submit a patch for it. I haven't looked at that one.
Quoted 2 lines
- Is there much point in making
CONFIG_PERFCTR_VIRTUALoptional?
It slows down an important fast path (context switch)
But it would be better to use some back patching design like kernel hooks to keep the cost for the common case (no perfctr getting switched) low. If that common case can be kept at a "no checks at all" level then it's good. That would be best for distribution kernels too.
-Andi