Eric Dumazet wrote:
> for umask/getppid(), its a basic loop with 100.000.000 iterations
Ah, OK, so there's about 2.5-3.5ns difference due to the instructions
you removed. That's very much in line with that I saw in my measurements.
> for read/write(), loop with 10.000.000 iterations
2 syscalls/iteration? It's interesting you measured about the same
absolute time difference (.42s) even though you're doing 1/5th the
number of syscalls.
> elapsed time (/usr/bin/time ./prog)
> 10 runs, and the minimum time is taken.
Hm, but "time" measures user, system and real time. You used real time?
> Hum... Do you mean a cache miss every time we do a syscall ? What
> could invalidate this cache exactly ?
Well, there might be a miss simply because the line got evicted. But as
Andi pointed out, a hot benchmark like this is very unlikely to get any
cache misses unless there's something very unfortunate happening.
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