Messages in this thread | | | Date | Tue, 10 Apr 2001 14:32:16 +0200 | From | Andi Kleen <> | Subject | Re: No 100 HZ timer ! |
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On Tue, Apr 10, 2001 at 01:12:14PM +0100, Alan Cox wrote: > Measure the number of clocks executing a timer interrupt. rdtsc is fast. Now > consider the fact that out of this you get KHz or better scheduling > resolution required for games and midi. I'd say it looks good. I agree
And measure the number of cycles a gigahertz CPU can do between a 1ms timer. And then check how often the typical application executes something like gettimeofday.
> the accounting of user/system time needs care to avoid slowing down syscall > paths
It's also all interrupts, not only syscalls, and also context switch if you want to be accurate.
On modern PC hardware it might be possible to do user/system accounting using performance MSRs. They have a bit in the performance counter that allows to only account user or system. If you find a count that is near equivalent to the cycles you have both: total = rdtsc, user = msr, system = rdtsc-msr. At least PPro derived have event 0x16, number of instructions executed, which might be good enough when multiplied with a factor if your instruction mix is not too unusual.
Still even with that the more complex checking in add_timer doesn't look too good.
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