Re: [PATCH] [RFC] Optimize select/poll by putting small data sets on the stack

[Eric Dumazet <dada1@cosmosbay.com>]

Andi Kleen a écrit :
> This is a RFC for now. I would be interested in testing
> feedback. Patch is for 2.6.15.
> 
> Optimize select and poll by a using stack space for small fd sets
> 
> This brings back an old optimization from Linux 2.0. Using
> the stack is faster than kmalloc. On a Intel P4 system
> it speeds up a select of a single pty fd by about 13%
> (~4000 cycles -> ~3500)

Was this result on UP or SMP kernel ? Preempt or not ?

I think we might play in do_pollfd() and use fget_light()/fput_light() instead 
of fget()/fput() that are somewhat expensive because of atomic inc/dec on SMP.

(I believe that select()/poll() based daemons are mostly non multi-threaded, 
since high performance multi-threaded programs should be using epoll...)

Eric