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Subjectsendfile()
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OK, I did some benchmarking on that beast (what else is new, I hear
you ask :))

I copied all 600MB worth of files from a IDE CD (24x) to /dev/null
using standard cp utility and cp imitation using sendfile() system
call instead of read()/write().

Results are as follows:

sendfile cp:
0.73user 34.23sys 3:42.18real 15%CPU (170120major+4636minor)pagefaults 25swaps

standard cp:
3.07user 156.15sys 3:44.34real 70%CPU (172868major+4878minor)pagefaults 25swaps

Wallclock times are equal since we're bound with the speed of CD-ROM
drive, but look at the CPU utilization. We have a clear winner, here.

What bothers me is that even though sendfile uses much less CPU time,
machine in fact becomes unusable while a program using it is running.
When using standard cp you barely notice slowdown, but sendfile()
definitely kills interactive feel.

Is there maybe a subtle bug in sendfile() implementation?
Or could it be that kernel incorectly measures and reports CPU usage?
Something else?

Pavel, if I recall correctly, you once had a patch you used to improve
kernel fairness in reporting CPU usage.

Could you be so kind and send me a copy, and spare me losing myself in
the archives. Also, I would like to have a recent version, for
2.1.115, if possible.

Thanks!
--
Posted by Zlatko Calusic E-mail: <Zlatko.Calusic@CARNet.hr>
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