re: [PATCH] up to 50% faster sys_poll()

[Dan Kegel <dank@alumni.caltech.edu>]

Manfred (manfred@colorfullife.com) wrote:
> sys_poll spends around 1/2 of the execution time allocating / freeing a 
> few bytes temporary memory. 
> The attached patch tries to avoid these allocation by using the stack - 
> usually only a few bytes are needed, kmalloc is used for the rest. 
> The result: one poll of stdin is down from 1736 cpu ticks to 865 cpu 
> ticks (Pentium II/350 SMP, SMP kernel) 

Tested with poll() microbenchmark from 
http://www.kegel.com/dkftpbench/Poller_bench.html

time in microsec to find a single active pipe among N pipes
on a 650 MHz dual Pentium III using poll():

                number of pipes
kernel        100    1000   10000
---------------------------------
2.4.0-t10pre4  49    1184   14660
2.4.0          48    1162   14702
2.4.0-pp       48    1103   14205

2.4.0-pp is with Manfred's patch.  Seems to be a 4-6% improvement 
for large numbers of pipes, no change for 100 pipes.

Hope that was an appropriate test. 

- Dan
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