diff options
| -rw-r--r-- | arch/x86/kernel/alternative.c | 16 | ||||
| -rw-r--r-- | include/linux/smp.h | 2 | ||||
| -rw-r--r-- | init/main.c | 16 |
3 files changed, 24 insertions, 10 deletions
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index cdc43242da92..318a4f9b7ece 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -273,6 +273,7 @@ struct smp_alt_module { }; static LIST_HEAD(smp_alt_modules); static DEFINE_SPINLOCK(smp_alt); +static int smp_mode = 1; /* protected by smp_alt */ void alternatives_smp_module_add(struct module *mod, char *name, void *locks, void *locks_end, @@ -354,7 +355,14 @@ void alternatives_smp_switch(int smp) BUG_ON(!smp && (num_online_cpus() > 1)); spin_lock_irqsave(&smp_alt, flags); - if (smp) { + + /* + * Avoid unnecessary switches because it forces JIT based VMs to + * throw away all cached translations, which can be quite costly. + */ + if (smp == smp_mode) { + /* nothing */ + } else if (smp) { printk(KERN_INFO "SMP alternatives: switching to SMP code\n"); clear_cpu_cap(&boot_cpu_data, X86_FEATURE_UP); clear_cpu_cap(&cpu_data(0), X86_FEATURE_UP); @@ -369,6 +377,7 @@ void alternatives_smp_switch(int smp) alternatives_smp_unlock(mod->locks, mod->locks_end, mod->text, mod->text_end); } + smp_mode = smp; spin_unlock_irqrestore(&smp_alt, flags); } @@ -441,7 +450,10 @@ void __init alternative_instructions(void) alternatives_smp_module_add(NULL, "core kernel", __smp_locks, __smp_locks_end, _text, _etext); - alternatives_smp_switch(0); + + /* Only switch to UP mode if we don't immediately boot others */ + if (num_possible_cpus() == 1 || setup_max_cpus <= 1) + alternatives_smp_switch(0); } #endif apply_paravirt(__parainstructions, __parainstructions_end); diff --git a/include/linux/smp.h b/include/linux/smp.h index c25e66bcecf3..55232ccf9cfd 100644 --- a/include/linux/smp.h +++ b/include/linux/smp.h @@ -78,6 +78,8 @@ int on_each_cpu(void (*func) (void *info), void *info, int retry, int wait); */ void smp_prepare_boot_cpu(void); +extern unsigned int setup_max_cpus; + #else /* !SMP */ /* diff --git a/init/main.c b/init/main.c index 3f8aba291ed3..5843fe996703 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(); |