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authorAndi Kleen <ak@suse.de>2008-01-30 13:33:17 +0100
committerIngo Molnar <mingo@elte.hu>2008-01-30 13:33:17 +0100
commitca74a6f84e68b44867022f4a4f3ec17c087c864e (patch)
treea5e84b251b1574b09288fb2636b4e4ea088ae70e /init
parent751752789162fde69474edfa15935d0a77c0bc17 (diff)
downloadlinux-ca74a6f84e68b44867022f4a4f3ec17c087c864e.tar.gz
x86: optimize lock prefix switching to run less frequently
On VMs implemented using JITs that cache translated code changing the lock prefixes is a quite costly operation that forces the JIT to throw away and retranslate a lot of code. Previously a SMP kernel would rewrite the locks once for each CPU which is quite unnecessary. This patch changes the code to never switch at boot in the normal case (SMP kernel booting with >1 CPU) or only once for SMP kernel on UP. This makes a significant difference in boot up performance on AMD SimNow! Also I expect it to be a little faster on native systems too because a smp switch does a lot of text_poke()s which each synchronize the pipeline. v1->v2: Rename max_cpus v1->v2: Fix off by one in UP check (Thomas Gleixner) Signed-off-by: Andi Kleen <ak@suse.de> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'init')
-rw-r--r--init/main.c16
1 files changed, 8 insertions, 8 deletions
diff --git a/init/main.c b/init/main.c
index 3f8aba291ed..5843fe99670 100644
--- a/init/main.c
+++ b/init/main.c
@@ -128,7 +128,7 @@ static char *ramdisk_execute_command;
#ifdef CONFIG_SMP
/* Setup configured maximum number of CPUs to activate */
-static unsigned int __initdata max_cpus = NR_CPUS;
+unsigned int __initdata setup_max_cpus = NR_CPUS;
/*
* Setup routine for controlling SMP activation
@@ -146,7 +146,7 @@ static inline void disable_ioapic_setup(void) {};
static int __init nosmp(char *str)
{
- max_cpus = 0;
+ setup_max_cpus = 0;
disable_ioapic_setup();
return 0;
}
@@ -155,8 +155,8 @@ early_param("nosmp", nosmp);
static int __init maxcpus(char *str)
{
- get_option(&str, &max_cpus);
- if (max_cpus == 0)
+ get_option(&str, &setup_max_cpus);
+ if (setup_max_cpus == 0)
disable_ioapic_setup();
return 0;
@@ -164,7 +164,7 @@ static int __init maxcpus(char *str)
early_param("maxcpus", maxcpus);
#else
-#define max_cpus NR_CPUS
+#define setup_max_cpus NR_CPUS
#endif
/*
@@ -393,7 +393,7 @@ static void __init smp_init(void)
/* FIXME: This should be done in userspace --RR */
for_each_present_cpu(cpu) {
- if (num_online_cpus() >= max_cpus)
+ if (num_online_cpus() >= setup_max_cpus)
break;
if (!cpu_online(cpu))
cpu_up(cpu);
@@ -401,7 +401,7 @@ static void __init smp_init(void)
/* Any cleanup work */
printk(KERN_INFO "Brought up %ld CPUs\n", (long)num_online_cpus());
- smp_cpus_done(max_cpus);
+ smp_cpus_done(setup_max_cpus);
}
#endif
@@ -824,7 +824,7 @@ static int __init kernel_init(void * unused)
__set_special_pids(1, 1);
cad_pid = task_pid(current);
- smp_prepare_cpus(max_cpus);
+ smp_prepare_cpus(setup_max_cpus);
do_pre_smp_initcalls();