Messages in this thread | | | From | Andrew Theurer <> | Subject | Re: 2.6.8-rc2-mm2 performance improvements (scheduler?) | Date | Mon, 9 Aug 2004 23:08:56 -0500 |
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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
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