[PATCH] x86: Don't use MWAIT on AMD Family 10

It doesn't put the CPU into deeper sleep states, so it's better to use the standard
idle loop to save power. But allow to reenable it anyways for benchmarking.

I also removed the obsolete idle=halt on i386

Cc: andreas.herrmann@amd.com
Signed-off-by: Andi Kleen <ak@suse.de>

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 4287696f18dd00c53e42989414234d41c88f7c24..94ce0d20253d8464ba17460c50b5dd6e9d12311b 100644 (file)
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -695,8 +695,15 @@ and is between 256 and 4096 characters. It is defined in the file
        idebus=         [HW] (E)IDE subsystem - VLB/PCI bus speed
                        See Documentation/ide.txt.
 
-       idle=           [HW]
-                       Format: idle=poll or idle=halt
+       idle=           [X86]
+                       Format: idle=poll or idle=mwait
+                       Poll forces a polling idle loop that can slightly improves the performance
+                       of waking up a idle CPU, but will use a lot of power and make the system
+                       run hot. Not recommended.
+                       idle=mwait. On systems which support MONITOR/MWAIT but the kernel chose
+                       to not use it because it doesn't save as much power as a normal idle
+                       loop use the MONITOR/MWAIT idle loop anyways. Performance should be the same
+                       as idle=poll.
 
        ignore_loglevel [KNL]
                        Ignore loglevel setting - this will print /all/

diff --git a/arch/i386/kernel/cpu/amd.c b/arch/i386/kernel/cpu/amd.c
index 2d47db48297218ee61c6b7b09576aa538561e97a..197cda62caa302cbfc6c9873494b4ccc1633beb1 100644 (file)
--- a/arch/i386/kernel/cpu/amd.c
+++ b/arch/i386/kernel/cpu/amd.c
@@ -53,6 +53,8 @@ static __cpuinit int amd_apic_timer_broken(void)
        return 0;
 }
 
+int force_mwait __cpuinitdata;
+
 static void __cpuinit init_amd(struct cpuinfo_x86 *c)
 {
        u32 l, h;
@@ -275,6 +277,9 @@ static void __cpuinit init_amd(struct cpuinfo_x86 *c)
 
        if (amd_apic_timer_broken())
                set_bit(X86_FEATURE_LAPIC_TIMER_BROKEN, c->x86_capability);
+
+       if (c->x86 == 0x10 && !force_mwait)
+               clear_bit(X86_FEATURE_MWAIT, c->x86_capability);
 }
 
 static unsigned int __cpuinit amd_size_cache(struct cpuinfo_x86 * c, unsigned int size)

diff --git a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c
index 393a67d5d9434807ead8524b91aa3094ccd54238..7e8e129b3d7db7d5729d06c8479c4da7093036bf 100644 (file)
--- a/arch/i386/kernel/process.c
+++ b/arch/i386/kernel/process.c
@@ -272,25 +272,24 @@ void __devinit select_idle_routine(const struct cpuinfo_x86 *c)
        }
 }
 
-static int __init idle_setup (char *str)
+static int __init idle_setup(char *str)
 {
-       if (!strncmp(str, "poll", 4)) {
+       if (!strcmp(str, "poll")) {
                printk("using polling idle threads.\n");
                pm_idle = poll_idle;
 #ifdef CONFIG_X86_SMP
                if (smp_num_siblings > 1)
                        printk("WARNING: polling idle and HT enabled, performance may degrade.\n");
 #endif
-       } else if (!strncmp(str, "halt", 4)) {
-               printk("using halt in idle threads.\n");
-               pm_idle = default_idle;
-       }
+       } else if (!strcmp(str, "mwait"))
+               force_mwait = 1;
+       else
+               return -1;
 
        boot_option_idle_override = 1;
-       return 1;
+       return 0;
 }
-
-__setup("idle=", idle_setup);
+early_param("idle", idle_setup);
 
 void show_regs(struct pt_regs * regs)
 {

diff --git a/arch/x86_64/kernel/process.c b/arch/x86_64/kernel/process.c
index d8d5ccc245c8977eaa1c616b9301df058661d386..4f21765078b7a1520aceb07be78095e76b525f3e 100644 (file)
--- a/arch/x86_64/kernel/process.c
+++ b/arch/x86_64/kernel/process.c
@@ -288,16 +288,18 @@ void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)
 
 static int __init idle_setup (char *str)
 {
-       if (!strncmp(str, "poll", 4)) {
+       if (!strcmp(str, "poll")) {
                printk("using polling idle threads.\n");
                pm_idle = poll_idle;
-       }
+       } else if (!strcmp(str, "mwait"))
+               force_mwait = 1;
+       else
+               return -1;
 
        boot_option_idle_override = 1;
-       return 1;
+       return 0;
 }
-
-__setup("idle=", idle_setup);
+early_param("idle", idle_setup);
 
 /* Prints also some state that isn't saved in the pt_regs */ 
 void __show_regs(struct pt_regs * regs)

diff --git a/arch/x86_64/kernel/setup.c b/arch/x86_64/kernel/setup.c
index 0a1d539149dfb2c23065dbe398fc3ccf67eac936..db30b5bcef610d87022f25365a0c7a2e1a42249b 100644 (file)
--- a/arch/x86_64/kernel/setup.c
+++ b/arch/x86_64/kernel/setup.c
@@ -79,6 +79,8 @@ int bootloader_type;
 
 unsigned long saved_video_mode;
 
+int force_mwait __cpuinitdata;
+
 /* 
  * Early DMI memory
  */
@@ -604,6 +606,10 @@ static void __cpuinit init_amd(struct cpuinfo_x86 *c)
 
        /* RDTSC can be speculated around */
        clear_bit(X86_FEATURE_SYNC_RDTSC, &c->x86_capability);
+
+       /* Family 10 doesn't support C states in MWAIT so don't use it */
+       if (c->x86 == 0x10 && !force_mwait)
+               clear_bit(X86_FEATURE_MWAIT, &c->x86_capability);
 }
 
 static void __cpuinit detect_ht(struct cpuinfo_x86 *c)

diff --git a/include/asm-i386/processor.h b/include/asm-i386/processor.h
index 9d895cc2f31220f92b4b285ad193ee26eda9cc7e..882d3f8fbbacf144132175063e567f2edd3884ae 100644 (file)
--- a/include/asm-i386/processor.h
+++ b/include/asm-i386/processor.h
@@ -779,4 +779,6 @@ extern int sysenter_setup(void);
 extern void cpu_set_gdt(int);
 extern void cpu_init(void);
 
+extern int force_mwait;
+
 #endif /* __ASM_I386_PROCESSOR_H */

diff --git a/include/asm-x86_64/proto.h b/include/asm-x86_64/proto.h
index 3f8f285138d272d8d100ce18f6f65bb4e6e60cb1..98063bcb3b336f6c1a2d389f02c254c877736221 100644 (file)
--- a/include/asm-x86_64/proto.h
+++ b/include/asm-x86_64/proto.h
@@ -119,6 +119,8 @@ extern int gsi_irq_sharing(int gsi);
 
 extern void smp_local_timer_interrupt(void);
 
+extern int force_mwait;
+
 long do_arch_prctl(struct task_struct *task, int code, unsigned long addr);
 
 void i8254_timer_resume(void);