BFS vs. mainline scheduler benchmarks and measurements

Posted Sep 7, 2009 3:41 UTC (Mon) by Baylink (guest, #755)
In reply to: BFS vs. mainline scheduler benchmarks and measurements by sbergman27
Parent article: BFS vs. mainline scheduler benchmarks and measurements

He said 'hyperthreaded'.

Doesn't that make it a 16-core?

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BFS vs. mainline scheduler benchmarks and measurements

Posted Sep 7, 2009 4:05 UTC (Mon) by Tracey (guest, #30515) [Link]

Baylink asked about 16 core.

We are looking to build a relatively inexpensive machine using a motherboard that can use two quad cores. This is pretty much what Ingo did his tests on(i7/i5s are hyperthreaded).

This machine will be used for compiling and desktop use.

There are wonderful people putting time and energy into the handhelds. Maybe these parties aretalking about fixing two completely different things then?

BFS vs. mainline scheduler benchmarks and measurements

Posted Sep 7, 2009 12:11 UTC (Mon) by nix (subscriber, #2304) [Link] (2 responses)

Yes, I'd say it does. The shared caches should affect scheduling decisions (but of course in BFS they don't :) ), and other shared resources (that is to say, pretty much all of them) would affect speed directly, but still you have to schedule 16 entities at once. They're just not symmetrical entities anymore. (In fact if it was dual-die you're into NUMA land, which means BFS is bound not to work well on it as it has no NUMA-awareness by design. I suspect my single-die quad Nehalem would work much better with it.)

[updated, quad core results] BFS vs. mainline scheduler benchmarks and measurements

Posted Sep 7, 2009 12:28 UTC (Mon) by mingo (subscriber, #31122) [Link] (1 responses)

Today i've measured and posted single-socket non-NUMA quad-core results as well:

"[quad core results] BFS vs. mainline scheduler benchmarks and measurements "

As the graphs show it, the quad results are similar to the 8-core results. So it wasnt NUMA or 16 cpus that made the difference.

Btw., you'd be wrong to treat an 8 core box with HyperThreading as a 16 core box. The physical resources are in essence that of an 8 core one - it's just more spreadable.

BFS should have no design disadvantage from HyperThreading, as siblings share the cache.

[updated, quad core results] BFS vs. mainline scheduler benchmarks and measurements

Posted Sep 7, 2009 14:13 UTC (Mon) by nix (subscriber, #2304) [Link]

Interesting.

(With regard to hyperthreading you are of course right that the physical resources are those of the physical cores, but surely unless you are HT-aware you will get lower performance on an HT system than otherwise, because you won't know to e.g. schedule threads of the same process on the same physical core if possible, to maximize cache sharing. But I know you know all this as the current mainline scheduler does it :) )