Re: Why do threads take so long to wake up underlinux

[Jim Hazen]

That's a good point.  However on my Dual 450 there seems to be no performance loss with these new settings.  In fact things seem a bit more responsive.  I'm not sure exactly why, but my guess would be extensive use of 'wait and notify' in various programs.  Before there was a 10ms penalty if one wanted to use this mechanism, now there isn't (but with the risk of many more context switches). My experience seems to indicate that this penalty outweighs the savings of fewer switches.

-Jim

The downside for sure it that you now interrupt the cpu 1000 times per
second. The overhead in processing the interrupt. ( context save,
registers saved ). The services performed at a clock ( jiffy ) tick (
timeout services, scheduling services ), are now done more frequently.
but with 1 gighz machine, 1/1000sec is ~1million instructions before an
jiffy happens. So if your threads complete before the million, then u r
in great shape. If they take longer, then that task may be scheduled out
to some other task that is also ready to run. I am not sure if a
Threaded task total quantum(s) are include in scheduling priority, or
each thread has their own unique scheduling priority.

/gat

BTW rumor has it ( from the Dec Alpha folks ) that context switching is
not very efficient on intel processors.