linux-kernel - [PATCH] Don't export sched_mc_power_savings on multi-socket single core system

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Date:	Wed, 08 Apr 2009 16:55:23 +0530
From:	Mahesh Jagannath Salgaonkar <mahesh@...ux.vnet.ibm.com>
To:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Suresh B Siddha <suresh.b.siddha@...el.com>,
	Ingo Molnar <mingo@...e.hu>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>
CC:	svaidy@...ux.vnet.ibm.com, balbir@...ux.vnet.ibm.com,
	dipankar@...ibm.com, Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: [PATCH] Don't export sched_mc_power_savings on multi-socket single
 core system

Fix to prevent sched_mc_power_saving from being exported through sysfs
for multi-scoket single core system. Max cores should be always greater than
one (1). My earlier patch that introduced fix for not exporting
'sched_mc_power_saving' on laptops  broke it on multi-socket single core
system. This fix addresses issue on both laptop and multi-socket single 
core system.
Below are the Test results:

1. Single socket - multi-core
       Before Patch: Does not export 'sched_mc_power_saving'
       After Patch: Does not export 'sched_mc_power_saving'
       Result: Pass

2. Multi Socket - single core
      Before Patch: exports 'sched_mc_power_saving'
      After Patch: Does not export 'sched_mc_power_saving'
      Result: Pass

3. Multi Socket - Multi core
      Before Patch: exports 'sched_mc_power_saving'
      After Patch: exports 'sched_mc_power_saving'


Signed-off-by: Mahesh Salgaonkar <mahesh@...ux.vnet.ibm.com>

Index: linux-2.6/arch/x86/include/asm/topology.h
===================================================================
--- linux-2.6.orig/arch/x86/include/asm/topology.h
+++ linux-2.6/arch/x86/include/asm/topology.h
@@ -203,7 +203,8 @@ struct pci_bus;
 void set_pci_bus_resources_arch_default(struct pci_bus *b);

 #ifdef CONFIG_SMP
-#define mc_capable()   (cpumask_weight(cpu_core_mask(0)) != nr_cpu_ids)
+#define mc_capable()   (boot_cpu_data.x86_max_cores > 1) && \
+                       (cpumask_weight(cpu_core_mask(0)) != nr_cpu_ids)
 #define smt_capable()                  (smp_num_siblings > 1)
 #endif
--
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