Re: Linus on Linux, Apache and Threads

Andi Kleen (ak@muc.de)
Sat, 24 Apr 1999 14:37:03 +0200

On Sat, Apr 24, 1999 at 02:35:59PM +0200, Alex Belits wrote:
> On 24 Apr 1999, Andi Kleen wrote:
>
> >
> > You have multiple threads doing an accept on a single listen socket. As
> > soon as a thread finished work it calls accept and gets the next ready
> > connection handed from the kernel.
>
> ...or will be awakened on the connection that was handled by another
> thread (because of "wake everyone" handling), and accept() will fail,
> causing the infamous "thundering herd".

If the load is high enough it doesn't matter, because there will
be always enough connections to be returned to an accept after a wakeup.
If it isn't the threads pool should adapt and use less threads which
avoids the problem (and a few lost wakeups in the transitions don't harm,
because the machine has enough free cycles).

Do you have any real data that this doesn't happen?

-Andi

-- 
This is like TV. I don't like TV.


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