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SubjectRe: async I/O seems to be blocking on 2.6.15
On Fri, 3 Nov 2006, Jens Axboe wrote:

> Try to time it (visual output of the app is not very telling, and it's
> buffered) and then apply some profiling.

OK, a little more info. I added gettimeofday() calls after each call
to io_submit(), put the timevals in an array, and after everything was
done computed the difference between each timeval and the program start
time, as well as the deltas. I got this:

0: 0.080s
1: 0.086s 0.006s
2: 0.102s 0.016s
3: 0.111s 0.008s
4: 0.118s 0.007s
5: 0.134s 0.015s
6: 0.141s 0.006s
7: 0.148s 0.006s
8: 0.158s 0.009s
9: 0.164s 0.006s
...
96: 1.036s 0.007s
97: 1.044s 0.007s
98: 1.147s 0.102s
99: 1.155s 0.008s

98 appears to be an aberration. Perhaps three of the times on an
average run are around a tenth of a second; all of the others are
pretty steady at 7 or 8 microseconds. So, it's basically linear in
its time consumption.

Does 7 microseconds seem a bit excessive for an io_submit (and a
gettimeofday)?



-bwb

Brent Baccala
cosine@freesoft.org
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