Re: Linux 2.6 context switching and posix threads performance question

[Christoph Lameter]

On Sat, 27 Aug 2005, Mateusz Berezecki wrote:

> I would really appreciate any comment on the overall performance of task
> switching with 25 000 threads running on the Linux system. I was asked to work
> on some software which spawns 25 000 threads and I am really worried if
> it will ever work on 2 CPU HP Blade. The kernel was modified to support
> bigger threads amount running (I have no idea how it was done, probably
> just changing hardcoded limits) What is the performance impact of
> so much threads on the overall system performance? Is there any ?
> Wouldn't it be that such application would spend all of its time
> switching contexts ? I'm asking for some kind of an authoritative answer
> quite urgently. What is the optimum thread amount on 2 CPU SMP system
> running Linux ?

At 32k threads you run into the limit of waiters for RW semaphores. So 
make sure that the number stays lower than that or use a 64 bit platform 
that supports more threads.

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