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Message-Id: <200704102011.18752.ak@suse.de>
Date: Tue, 10 Apr 2007 20:11:18 +0200
From: Andi Kleen <ak@...e.de>
To: "Andreas Herrmann" <andreas.herrmann3@....com>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86_64: prevent auto select of mwait_idle for AMD CPUs
On Tuesday 10 April 2007 19:24:25 Andreas Herrmann wrote:
> This fix is needed for AMD family 10h CPUs.
>
> It prevents auto select of mwait_idle for AMD CPUs.
> MWAIT does not enter C-states on family 10h and more
> power saving is reached by entering C1 with
> default_idle.
>
> The patch also adds an idle=mwait command line option
> to select mwait_idle for benchmarking.
I already did my own patch earlier. Applied for reference.
-Andi
Don't use MWAIT on AMD Family 10/11
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
Signed-off-by: Andi Kleen <ak@...e.de>
Index: linux/Documentation/kernel-parameters.txt
===================================================================
--- linux.orig/Documentation/kernel-parameters.txt
+++ linux/Documentation/kernel-parameters.txt
@@ -673,8 +673,15 @@ and is between 256 and 4096 characters.
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/
Index: linux/arch/i386/kernel/cpu/amd.c
===================================================================
--- linux.orig/arch/i386/kernel/cpu/amd.c
+++ linux/arch/i386/kernel/cpu/amd.c
@@ -22,6 +22,8 @@
extern void vide(void);
__asm__(".align 4\nvide: ret");
+int force_mwait __initdata;
+
static void __cpuinit init_amd(struct cpuinfo_x86 *c)
{
u32 l, h;
@@ -241,6 +243,9 @@ static void __cpuinit init_amd(struct cp
if (cpuid_eax(0x80000000) >= 0x80000006)
num_cache_leaves = 3;
+
+ if ((c->x86 == 0x10 || c->x86 == 0x11) && !force_mwait)
+ clear_bit(X86_FEATURE_MWAIT, &c->x86_capability);
}
static unsigned int __cpuinit amd_size_cache(struct cpuinfo_x86 * c, unsigned int size)
Index: linux/arch/i386/kernel/process.c
===================================================================
--- linux.orig/arch/i386/kernel/process.c
+++ linux/arch/i386/kernel/process.c
@@ -272,25 +272,24 @@ void __devinit select_idle_routine(const
}
}
-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)
{
Index: linux/arch/x86_64/kernel/process.c
===================================================================
--- linux.orig/arch/x86_64/kernel/process.c
+++ linux/arch/x86_64/kernel/process.c
@@ -288,16 +288,18 @@ void __cpuinit select_idle_routine(const
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)
Index: linux/arch/x86_64/kernel/setup.c
===================================================================
--- linux.orig/arch/x86_64/kernel/setup.c
+++ linux/arch/x86_64/kernel/setup.c
@@ -79,6 +79,8 @@ int bootloader_type;
unsigned long saved_video_mode;
+int force_mwait __initdata;
+
/*
* Early DMI memory
*/
@@ -604,6 +606,10 @@ static void __cpuinit init_amd(struct cp
/* RDTSC can be speculated around */
clear_bit(X86_FEATURE_SYNC_RDTSC, &c->x86_capability);
+
+ /* Family 10/11 don't support C states in MWAIT so don't use it */
+ if ((c->x86 == 0x10 || c->x86 == 0x11) && !force_mwait)
+ clear_bit(X86_FEATURE_MWAIT, &c->x86_capability);
}
static void __cpuinit detect_ht(struct cpuinfo_x86 *c)
Index: linux/include/asm-i386/processor.h
===================================================================
--- linux.orig/include/asm-i386/processor.h
+++ linux/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 */
Index: linux/include/asm-x86_64/proto.h
===================================================================
--- linux.orig/include/asm-x86_64/proto.h
+++ linux/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);
-
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