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x86, hotplug: Fix powersavings with offlined cores on AMD 

ea53069231 made a CPU use monitor/mwait
when offline. This is not the optimal choice for AMD wrt to powersavings
and we'd prefer our cores to halt (i.e. enter C1) instead. For this, the
same selection whether to use monitor/mwait has to be used as when we
select the idle routine for the machine.

With this patch, offlining cores 1-5 on a X6 machine allows core0 to
boost again.

[ hpa: putting this in urgent since it is a (power) regression fix ]

Reported-by: Andreas Herrmann <andreas.herrmann3@amd.com>
Cc: stable@kernel.org # 37.x
Cc: H. Peter Anvin <hpa@linux.intel.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Len Brown <lenb@kernel.org>
Cc: Venkatesh Pallipadi <venki@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.hl>
Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
LKML-Reference: <1295534572-10730-1-git-send-email-bp@amd64.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Borislav Petkov 2011-01-20 15:42:52 +01:00 committed by H. Peter Anvin
parent f21bbec9ff
commit 93789b32db
3 changed files with 5 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
arch/x86/include/asm/cpu.h
View File

@ -32,5 +32,6 @@ extern void arch_unregister_cpu(int);
DECLARE_PER_CPU(int, cpu_state);
int __cpuinit mwait_usable(const struct cpuinfo_x86 *);
#endif /* _ASM_X86_CPU_H */

3
arch/x86/kernel/process.c
View File

@ -14,6 +14,7 @@
#include <linux/utsname.h>
#include <trace/events/power.h>
#include <linux/hw_breakpoint.h>
#include <asm/cpu.h>
#include <asm/system.h>
#include <asm/apic.h>
#include <asm/syscalls.h>
@ -505,7 +506,7 @@ static void poll_idle(void)
#define MWAIT_ECX_EXTENDED_INFO 0x01
#define MWAIT_EDX_C1 0xf0
static int __cpuinit mwait_usable(const struct cpuinfo_x86 *c)
int __cpuinit mwait_usable(const struct cpuinfo_x86 *c)
{
u32 eax, ebx, ecx, edx;

3
arch/x86/kernel/smpboot.c
View File

@ -1402,8 +1402,9 @@ static inline void mwait_play_dead(void)
unsigned int highest_subcstate = 0;
int i;
void *mwait_ptr;
struct cpuinfo_x86 *c = __this_cpu_ptr(&cpu_info);
if (!cpu_has(__this_cpu_ptr(&cpu_info), X86_FEATURE_MWAIT))
if (!(cpu_has(c, X86_FEATURE_MWAIT) && mwait_usable(c)))
return;
if (!cpu_has(__this_cpu_ptr(&cpu_info), X86_FEATURE_CLFLSH))
return;