Re: PowerPC fastpaths for mutex subsystem

[Joel Schopp <jschopp@austin.ibm.com>]

> interesting. Could you try two things? Firstly, could you add some 
> minimal delays to the lock/unlock path, of at least 1 usec? E.g.  
> "synchro-test.ko load=1 interval=1". [but you could try longer delays 
> too, 10 usecs is still realistic.]

Graphs attached.  The summary for those who don't like to look at attachments is 
that the mutex fastpath (threads 1) that I sent the optimized patch for is 
comparable within the margin of error to semaphores.  The mutex common path 
(threads > 1) gets embarrassed by semaphores. So mutexes common paths are not 
yet ready as far as ppc64 is concerned.

> secondly, could you try the VFS creat+unlink test via the test-mutex.c 
> code below, with something like:
>
> 	./test-mutex V 16 10

Queued into my todo list.

> thirdly, could you run 'vmstat 1' during the tests, and post those lines 
> too? Here i'm curious about two things: the average runqueue length 
> (whether we have overscheduling), and CPU utilization and idle time left 
> (how efficiently cycles are preserved in contention). [btw., does ppc 
> have an idle=poll equivalent mode of idling?]

Also queued in my todo list.

> also, there seems to be some fluctuation in the numbers - could you try 
> to run a few more to see how stable the numbers are?

For the graphs the line is the average of 5 runs, and the 5 runs are scatter 
plotted as well.