Re: [PATCH] poll: Avoid extra wakeups in select/poll

Ingo Molnar
2009-04-29T09:12:44Z

* Eric Dumazet <dada1@cosmosbay.com> wrote:

> On uddpping, I had prior to the patch about 49000 wakeups per
> second, and after patch about 26000 wakeups per second (matches
> number of incoming udp messages per second)

very nice. It might not show up as a real performance difference if
the CPUs are not fully saturated during the test - but it could show
up as a decrease in CPU utilization.

Also, if you run the test via 'perf stat -a ./test.sh' you should
see a reduction in instructions executed:

aldebaran:~/linux/linux> perf stat -a sleep 1

Performance counter stats for 'sleep':

16128.045994 task clock ticks (msecs)
12876 context switches (events)
219 CPU migrations (events)
186144 pagefaults (events)
20911802763 CPU cycles (events)
19309416815 instructions (events)
199608554 cache references (events)
19990754 cache misses (events)

Wall-clock time elapsed: 1008.882282 msecs

With -a it's measured system-wide, from start of test to end of test
- the results will be a lot more stable (and relevant) statistically
than wall-clock time or CPU usage measurements. (both of which are
rather imprecise in general)

Ingo