Re: multi-queue scheduler update

[Mike Kravetz]

On Fri, Jan 19, 2001 at 02:08:52AM +0100, Andi Kleen wrote:
> On Thu, Jan 18, 2001 at 08:00:16PM -0500, Mark Hahn wrote:
> > > >                            microseconds/yield
> > > > # threads      2.2.16-22           2.4        2.4-multi-queue
> > > > ------------   ---------         --------     ---------------
> > > > 16               18.740            4.603         1.455
> > > 
> > > I remeber the O(1) scheduler from Davide Libenzi was beating the mainline O(N)
> > 
> > isn't the normal case (as in "The Right Case to optimize") 
> > where there are close to zero runnable tasks?  what realistic/sane
> > scenarios have very large numbers of spinning threads?  all server
> > situations I can think of do not.  not volanomark -loopback, surely!
> 
> I think the main point of Mike's patch is decreasing locking and cache line
> bouncing overhead of multi cpu scheduling, not optimizing lots of runnable tasks.
> 
> 
> -Andi

Andi is correct.  Although the results I posted may seem to indicate
we are concentrating on high thread counts, this is really secondary
to reducing lock contention within the scheduler.  A co-worker down
the hall just ran pgbench (a postgresql db) benchmark and saw
contention on the runqueue lock at 57%.  Now, I know nothing about this
benchmark, but it will be interesting to see what happens after
applying my patch.

-- 
Mike Kravetz                                 [e-mail]
IBM Linux Technology Center