Re: [PATCH] Don't export sched_mc_power_savings in laptops

From: Mahesh Jagannath Salgaonkar
Date: Mon Dec 01 2008 - 01:50:43 EST

Ingo Molnar wrote:
* Mahesh Salgaonkar <mahesh@xxxxxxxxxxxxxxxxxx> wrote:

Fix to prevent sched_mc_power_saving from being exported through sysfs
for multicore single socket (Laptop).
CPU core map of the boot cpu should be equal to possible number
of cpus for single socket system.
This fix has been developed at kernel workout.
Signed-off-by: Mahesh Salgaonkar <mahesh@xxxxxxxxxxxxxxxxxx>

diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h
index 4850e4b..4adc830 100644
--- a/arch/x86/include/asm/topology.h
+++ b/arch/x86/include/asm/topology.h
@@ -239,7 +239,7 @@ struct pci_bus;
void set_pci_bus_resources_arch_default(struct pci_bus *b);
-#define mc_capable() (boot_cpu_data.x86_max_cores > 1)
+#define mc_capable() (cpus_weight(per_cpu(cpu_core_map,0)) != nr_cpu_ids)

hm, dunno. sched_mc_power_savings should have no effect on single-socket systems, right? So the knob should have no effect.

Hi Ingo,

Yes, it will not have any effect but it enables additional code path leading to an
overhead in case of single-socket system. This overhead is only if
"sched_mc_power_savings = 1", however we are still leaving it to zero (default) and
preventing user space from turning it on by mistake.


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