* Zach Brown <[EMAIL PROTECTED]> [010814 17:42] wrote:
> [pulls out his dead horse..]
>
> > > one thread would wake up. The mistake in your sample seems to be that
> > > you're having all threads block on the same fd. Why?
> >
> > Probably he has a bunch of daemons waiting around for work to
> > do (e.g. HTTP daemons all listening for connections to accept
> > on the same fd). Lot's of applications could use this model
> > to get a performance boost.
>
> I have yet to see a 'thundering accept()' actually shown to be a
> meaningful performance problem. Are there more than two significant
> situations here?
>
> a) you have lots of idle servers waiting for work on an fd. it arrives,
> they all wake up, only to find that one of them gets to do real work.
> Who cares? you were idle. you had time to kill. The time when this
> wouldn't be acceptable would be if there were _very_ tight response
> time constraints.
>
> b) you're under load. your servers are off doing work under that load.
> you rarely see a significant number of them waiting for new work at
> the same time. wakeups (or scheduling) don't make up a meaningful
> percentage of the real work (io, networking, app data crunching, etc)
> that is being done.
>
> "b)" was the case at the zdnet benchmarks, though people ran around
> screaming things about thundering accept()s apaches when not a one of
> them had profiling runs in front of them :)
>
> I'm not saying that wake-one isn't a fine idea, I just keep seeing
> references to the mystical thundering accept() wakeup problem and its
> solution that brings better performance. I keep asking when people
> mention it and no one has been able to show this to be the case based
> on numbers.
>
> Am I insane?
Not insane, just wrong.
Picture a moderately loaded server, this is where the superfluous
wakeups cause a moderately loaded server to go over the edge.
Here's a reference about this:
http://www.citi.umich.edu/projects/linux-scalability/reports/accept.html
Linux was only about 5 years behind in discovering/implementing
this. :)
--
-Alfred Perlstein [[EMAIL PROTECTED]]
Ok, who wrote this damn function called '??'?
And why do my programs keep crashing in it?
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