Messages in this thread | | | Subject | Re: change in sched cpu_power causing regressions with SCHED_MC | From | Peter Zijlstra <> | Date | Sat, 13 Feb 2010 11:36:28 +0100 |
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On Fri, 2010-02-12 at 17:31 -0800, Suresh Siddha wrote: > > We have one more problem that Yanmin and Ling Ma reported. On a dual > socket quad-core platforms (for example platforms based on NHM-EP), we > are seeing scenarios where one socket is completely busy (with all the 4 > cores running with 4 tasks) and another socket is completely idle. > > This causes performance issues as those 4 tasks share the memory > controller, last-level cache bandwidth etc. Also we won't be taking > advantage of turbo-mode as much as we like. We will have all these > benefits if we move two of those tasks to the other socket. Now both the > sockets can potentially go to turbo etc and improve performance. > > In short, your recent change (shown below) broke this behavior. In the > kernel summit you mentioned you made this change with out affecting the > behavior of SMT/MC. And my testing immediately after kernel-summit also > didn't show the problem (perhaps my test didn't hit this specific > change). But apparently we are having performance issues with this patch > (Ling Ma's bisect pointed to this patch). I will look more detailed into > this after the long weekend (to see if we can catch this scenario in > fix_small_imbalance() etc). But wanted to give you a quick heads up. > Thanks.
Right, so the behaviour we want should be provided by SD_PREFER_SIBLING, it provides the capacity==1 thing the cpu_power games used to provide.
Not saying it's not broken, but that's where the we should be looking to fix it.
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