epoll improvements

[michi1 at michaelblizek.twilightparadox.com]

Hi!

On 13:02 Thu 16 Oct     , Valdis.Kletnieks at vt.edu wrote:
> On Thu, 16 Oct 2014 14:09:05 +0200, "Nev Ikte" said:
> 
> > I've tried to reproduce it with a single client
> > and basically, if ep_poll() is able to find an event or the timeout is 0,
> > the latency is down to 5usec, otherwise if it enters the waitqueue
> > the latency goes up to 10-25usec, which impact the application performance.
> 
> Is it possible that what you're actually measuring here is your CPU's
> latency coming out of a sleep state if every task is in a wait queue?

I have seen wakeup latencies of ~100usec on some systems. You may want to
disable sleep states and see of performance gets better. Take a look at:

Documentation/power/pm_qos_interface.txt

Also, you probably want disable frequency scaling:

/sys/devices/system/cpu/cpu.../cpufreq/scaling_governor should return
"performance" for every cpu. You can change it with
eche "performance" > /sys/...

	-Michi
-- 
programing a layer 3+4 network protocol for mesh networks
see http://michaelblizek.twilightparadox.com