Messages in this thread | | | Date | Sat, 15 Sep 2012 00:14:40 +0200 | From | Borislav Petkov <> | Subject | Re: 20% performance drop on PostgreSQL 9.2 from kernel 3.5.3 to 3.6-rc5 on AMD chipsets - bisected |
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On Fri, Sep 14, 2012 at 03:01:44PM -0700, Linus Torvalds wrote: > On Fri, Sep 14, 2012 at 2:56 PM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: > > > > Both things change semantics, not looking at the entire package is new > > too. > > Well, the "idle_buddy" thing on its own could be considered to be > purely a caching thing. > > Sure, it doesn't take tsk_cpus_allowed() into account while setting up > the cache (since it's not dynamic enough), but *assuming* the common > case is that people let threads be on any of the cores of a package, > it should be possible to make the cache 100% equivalent with no > semantic change. No? > > The code doesn't even try to do that kind of "don't change semantics", > though, and makes the idle-buddy thing entirely different.
Could it be that this machine has a non-power of two cores (6) and maybe the idle buddy selection doesn't work as expected?
(Although it shouldn't since the commit message speaks also of non-power of two cores (40) and it works fine there).
Anyway, here's the topology of the box:
$ for i in $(ls cpu?/topology/*); do echo -n $i": "; cat $i; done cpu0/topology/core_id: 0 cpu0/topology/core_siblings: 3f cpu0/topology/core_siblings_list: 0-5 cpu0/topology/physical_package_id: 0 cpu0/topology/thread_siblings: 01 cpu0/topology/thread_siblings_list: 0 cpu1/topology/core_id: 1 cpu1/topology/core_siblings: 3f cpu1/topology/core_siblings_list: 0-5 cpu1/topology/physical_package_id: 0 cpu1/topology/thread_siblings: 02 cpu1/topology/thread_siblings_list: 1 cpu2/topology/core_id: 2 cpu2/topology/core_siblings: 3f cpu2/topology/core_siblings_list: 0-5 cpu2/topology/physical_package_id: 0 cpu2/topology/thread_siblings: 04 cpu2/topology/thread_siblings_list: 2 cpu3/topology/core_id: 3 cpu3/topology/core_siblings: 3f cpu3/topology/core_siblings_list: 0-5 cpu3/topology/physical_package_id: 0 cpu3/topology/thread_siblings: 08 cpu3/topology/thread_siblings_list: 3 cpu4/topology/core_id: 4 cpu4/topology/core_siblings: 3f cpu4/topology/core_siblings_list: 0-5 cpu4/topology/physical_package_id: 0 cpu4/topology/thread_siblings: 10 cpu4/topology/thread_siblings_list: 4 cpu5/topology/core_id: 5 cpu5/topology/core_siblings: 3f cpu5/topology/core_siblings_list: 0-5 cpu5/topology/physical_package_id: 0 cpu5/topology/thread_siblings: 20 cpu5/topology/thread_siblings_list: 5
-- Regards/Gruss, Boris.
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