On Mon, Sep 07 2009, Jens Axboe wrote:
> > And yes, it would be wonderful to get a test-app from you that would 
> > express the kind of pain you are seeing during compile jobs.
> 
> I was hoping this one would, but it's not showing anything. I even added
> support for doing the ping and wakeup over a socket, to see if the pipe
> test was doing well because of the sync wakeup we do there. The net
> latency is a little worse, but still good. So no luck in making that app
> so far.

Here's a version that bounces timestamps between a producer and a number
of consumers (clients). Not really tested much, but perhaps someone can
compare this on a box that boots BFS and see what happens.

To run it, use -cX where X is the number of children that you wait for a
response from. The max delay between this children is logged for each
wakeup. You can invoke it ala:

$ ./latt -c4 'make -j4'

and it'll dump the max/avg/stddev bounce time after make has completed,
or if you just want to play around, start the compile in one xterm and
do:

$ ./latt -c4 'sleep 5'

to just log for a small period of time. Vary the number of clients to
see how that changes the aggregated latency. 1 should be fast, adding
more clients quickly adds up.

Additionally, it has a -f and -t option that controls the window of
sleep time for the parent between each message. The numbers are in
msecs, and it defaults to a minimum of 100msecs and up to 500msecs.

-- 
Jens Axboe