Re: 2.6.8-rc2-mm2 performance improvements (scheduler?)

[Andrew Theurer <habanero@us.ibm.com>]

On Monday 09 August 2004 22:40, you wrote:
>    Rick showed me schedstats graphs of the two ... it seems to have lower
>     latency, does less rebalancing, fewer pull_tasks, etc, etc. Everything
>     looks better ... he'll send them out soon, I think (hint, hint).
>
> Okay, they're done. Here's the URL of the graphs:
>
>     http://eaglet.rain.com/rick/linux/staircase/scase-vs-noscase.html
>
> General summary: as Martin reported, we're seeing improvements in a number
> of areas, at least with sdet.  The graphs as listed there represent stats
> from four separate sdet runs run sequentially with an increasing load.
> (We're trying to see if we can get the information from each run
> separately, rather than the aggregate -- one of the hazards of an automated
> test harness :)

What's quite interesting is that there is a very noticeable surge in 
load_balance with staircase in the early stage of the test, but there appears 
to be -no- direct policy changes to load-balance at all in Con's patch (or at 
least I didn't notice it -please tell me if you did!).  You can see it in 
busy load_balance, sched_balance_exec, and pull_task.  The runslice and 
latency stats confirm this -no-staircase does not balance early on, and the 
tasks suffer, waiting on a cpu already loaded up.  I do not have an 
explanation for this; perhaps it has something to do with eliminating expired 
queue.

I would be nice to have per cpu runqueue lengths logged to see how this plays 
out -do the cpus on staircase obtain a runqueue length close to 
nr_running()/nr_online_cpus sooner than no-staircase?

Also, one big change apparent to me, the elimination of TIMESLICE_GRANULARITY.  
Do you have cswitch data?  I would not be surprised if it's a lot higher on 
-no-staircase, and cache is thrashed a lot more.  This may be something you 
can pull out of the -no-staircase kernel quite easily.

-Andrew Theurer