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SubjectRe: HZ=1000 & kernel profiling?
   From: Paul Gortmaker <paul@rasty.anu.edu.au>
Date: Sun, 19 Jan 1997 15:40:35 +1000 (EST)

(2) Use a sampling trigger that is comparable to 100Hz, but much
more independent of general kernel activity than the timer
interrupt, so that a functions execution time in relation
to the timer interrupt will not effect the profiling data.
In addition, you don't incurr the higher overhead of having
an excessive timer interrupt rate as in (1).

Some more ideas, something tells me that if you run a seperate timer
as you suggest, but make sure the profiling timer has the following
two qualities:

1) The rate of the profiling timer tick is relatively prime
to the rate of the normal tick

2) The profiling timer runs completely in assembler and does
not save/restore state, just records the profiling info
then returns from the trap, no c-code, smaller cache
footprint and less cycles burned, thus the changed timing
timing of the kernel caused by the profiling tick itself
is reduced as much as possible

you'd get much more desirable and accurate results.

Just some ideas.

---------------------------------------------////
Yow! 11.26 MB/s remote host TCP bandwidth & ////
199 usec remote TCP latency over 100Mb/s ////
ethernet. Beat that! ////
-----------------------------------------////__________ o
David S. Miller, davem@caip.rutgers.edu /_____________/ / // /_/ ><

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