Re: [PATCH] ARM64: Enable multi-core scheduler support by default
From: Catalin Marinas
Date: Fri Oct 30 2015 - 11:35:50 EST
On Fri, Oct 30, 2015 at 12:29:00PM +0000, Dietmar Eggemann wrote:
> On 10/29/2015 05:19 PM, Catalin Marinas wrote:
> >On Mon, Oct 19, 2015 at 05:55:49PM +0100, Dietmar Eggemann wrote:
> >>Make sure that the task scheduler domain hierarchy is set-up correctly
> >>on systems with single or multi-cluster topology.
> >>Signed-off-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
> >> arch/arm64/configs/defconfig | 1 +
> >> 1 file changed, 1 insertion(+)
> >>diff --git a/arch/arm64/configs/defconfig b/arch/arm64/configs/defconfig
> >>index 34d71dd86781..dc70d715bc38 100644
> >>--- a/arch/arm64/configs/defconfig
> >>+++ b/arch/arm64/configs/defconfig
> >>@@ -51,6 +51,7 @@ CONFIG_PCI=y
> >> CONFIG_PCI_MSI=y
> >> CONFIG_PCI_XGENE=y
> >> CONFIG_SMP=y
> >> CONFIG_PREEMPT=y
> >> CONFIG_KSM=y
> >> CONFIG_TRANSPARENT_HUGEPAGE=y
> >Question: does enabling this option have any (positive) effect on the
> >vanilla kernel or it requires additional patches like EAS?
> It improves the task scheduler decisions on multi-cluster systems. You have
> to iterate over all cpu's less frequently when gathering the sched group
> statistics e.g. during CFS load-balancing.
> You essentially replace a flat (all cpus) with an hierarchical approach
> (lowest level: sched group eq. cpu, next level: sched group eq. cluster) and
> do CFS load balancing frequently between two cpu's of the same cluster
> (lowest level) and less frequently between two cpus from different cluster.
> Not sure that I would see an effect on the performance score on a JUNO board
> when running hackbench. Could give it a try ... Probably easier to spot on a
> machine with >32 logical cpus.
I did some tests on Juno last week with and without this option and I
haven't noticed any difference.
Anyway, thanks for the explanation. Patch applied.
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