Re: Latch implementation

On 22/09/10 23:31, Ganesh Venkitachalam-1 wrote:
> I've been playing around with measuring the latch implementation in 9.1,
> and here are the results of a ping-pong test with 2 processes signalling
> and waiting on the latch. I did three variations (linux 2.6.18, nehalem
> processor).
>
> One is the current one.
>
> The second is built on native semaphors on linux. This one cannot
> implement WaitLatchOrSocket, there's no select involved.
>
> The third is an implementation based on pipe() and poll. Note: in its
> current incarnation it's essentially a hack to measure performance, it's
> not usable in postgres, this assumes all latches are created before any
> process is forked. We'd need to use mkfifo to sort that out if we really
> want to go this route, or similar.
>
> - Current implementation: 1 pingpong is avg 15 usecs
> - Pipe+poll: 9 usecs
> - Semaphore: 6 usecs
>
> The test program & modified unix_latch.c is attached, you can compile it
> like "gcc -DPIPE -O2 sema.c" or "gcc -DLINUX_SEM -O2 sema.c" or "gcc -O2
> sema.c".

Interesting, thanks for the testing! Could you also test how much faster 
the current implementation gets by just replacing select() with poll()? 
That should shave off some overhead.


--   Heikki Linnakangas  EnterpriseDB   http://www.enterprisedb.com