x86, hotplug: Fix powersavings with offlined cores on AMD

ea53069231f9317062910d6e772cca4ce93de8c8 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>

diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
index 4fab24de26b18404069994b908c79d3e4e481c50..6e6e7558e702cbdeb56a5fb7c5e048cb82f15e9b 100644 (file)
--- a/arch/x86/include/asm/cpu.h
+++ b/arch/x86/include/asm/cpu.h
@@ -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 */

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index d8286ed54ffaba86a0882baae443cd9d267b5a30..e764fc05d700365246d4e77f52a406bbfe1c7d22 100644 (file)
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -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;
 

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 763df77343dd99db4300a74304013ea685310f55..0cbe8c0b35edd290e98c989cfc48c5b4b0af350a 100644 (file)
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -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;