Re: condvar wakeups

Ingo Molnar wrote:
> 
> until someone can show some real degradation due to wakeup behavior i'll
> close this issue and wont pursue FUTEX_REQUEUE upstream, it seems to bring
> no benefits.
>  

This patch definitely helps on a 4-way system and it made a hugh
difference
in some of the results. There wasn't much of a problem on a UP and 2-way
systems earlier wrt to pthread_cond_broadcast and 200+ threads, so this 
patch has no impact in such cases. However, on a 4-way and above
systems, it
improves the pthread_cond_broadcast for 200+ threads in a big way.

Here are some of the results on a 4-way:
pingpong test:
./pp -v -n 128 -i 1 -S 32768
With OLD NPTL:
256 threads initialised in 0s.10090ms
128 games completed in 32s.250439ms

With requeue NPTL:
256 threads initialised in 0s.9938ms
128 games completed in 0s.5219ms

Same thing is true for all other cases, where n > 128.

Ulrich's cond-perf test:
There is not much of difference where n is less than 200.
./cond-perf -r 10 -n 200
OLD NPTL: Never completes, its looping somewhere
LinuxThreads: completes in 0m0.085s
requeue NPTL: completes in 0m0.027s

I can't compile this patch for an UP-system, so I don't have any
numbers.
Again, its a big win for 200+ threads, so this patch should go in.

- Saurabh