3.2.99-rc1 review patch. If anyone has any objections, please let me know.
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From: Rusty Russell rusty@rustcorp.com.au
commit 816afe4ff98ee10b1d30fd66361be132a0a5cee6 upstream.
We still patch SMP instructions to UP variants if we boot with a single CPU, but not at any other time. In particular, not if we unplug CPUs to return to a single cpu.
Paul McKenney points out:
mean offline overhead is 6251/48=130.2 milliseconds.
If I remove the alternatives_smp_switch() from the offline path [...] the mean offline overhead is 550/42=13.1 milliseconds
Basically, we're never going to get those 120ms back, and the code is pretty messy.
We get rid of:
1) The "smp-alt-once" boot option. It's actually "smp-alt-boot", the documentation is wrong. It's now the default.
2) The skip_smp_alternatives flag used by suspend.
3) arch_disable_nonboot_cpus_begin() and arch_disable_nonboot_cpus_end() which were only used to set this one flag.
Signed-off-by: Rusty Russell rusty@rustcorp.com.au Cc: Paul McKenney paul.mckenney@us.ibm.com Cc: Suresh Siddha suresh.b.siddha@intel.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Andrew Morton akpm@linux-foundation.org Cc: Peter Zijlstra a.p.zijlstra@chello.nl Link: http://lkml.kernel.org/r/87vcgwwive.fsf@rustcorp.com.au Signed-off-by: Ingo Molnar mingo@kernel.org [bwh: Backported to 3.2: adjust context] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- Documentation/kernel-parameters.txt | 3 - arch/x86/include/asm/alternative.h | 4 +- arch/x86/kernel/alternative.c | 107 +++++++++--------------------------- arch/x86/kernel/smpboot.c | 20 +------ arch/x86/xen/smp.c | 6 +- kernel/cpu.c | 11 ---- 6 files changed, 32 insertions(+), 119 deletions(-)
--- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -2440,9 +2440,6 @@ bytes respectively. Such letter suffixes smart2= [HW] Format: <io1>[,<io2>[,...,<io8>]]
- smp-alt-once [X86-32,SMP] On a hotplug CPU system, only - attempt to substitute SMP alternatives once at boot. - smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port smsc-ircc2.ircc_sir= [HW] SIR base I/O port --- a/arch/x86/include/asm/alternative.h +++ b/arch/x86/include/asm/alternative.h @@ -61,7 +61,7 @@ extern void alternatives_smp_module_add( void *locks, void *locks_end, void *text, void *text_end); extern void alternatives_smp_module_del(struct module *mod); -extern void alternatives_smp_switch(int smp); +extern void alternatives_enable_smp(void); extern int alternatives_text_reserved(void *start, void *end); extern bool skip_smp_alternatives; #else @@ -69,7 +69,7 @@ static inline void alternatives_smp_modu void *locks, void *locks_end, void *text, void *text_end) {} static inline void alternatives_smp_module_del(struct module *mod) {} -static inline void alternatives_smp_switch(int smp) {} +static inline void alternatives_enable_smp(void) {} static inline int alternatives_text_reserved(void *start, void *end) { return 0; --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -21,19 +21,6 @@
#define MAX_PATCH_LEN (255-1)
-#ifdef CONFIG_HOTPLUG_CPU -static int smp_alt_once; - -static int __init bootonly(char *str) -{ - smp_alt_once = 1; - return 1; -} -__setup("smp-alt-boot", bootonly); -#else -#define smp_alt_once 1 -#endif - static int __initdata_or_module debug_alternative;
static int __init debug_alt(char *str) @@ -438,9 +425,6 @@ static void alternatives_smp_unlock(cons { const s32 *poff;
- if (noreplace_smp) - return; - mutex_lock(&text_mutex); for (poff = start; poff < end; poff++) { u8 *ptr = (u8 *)poff + *poff; @@ -471,7 +455,7 @@ struct smp_alt_module { }; static LIST_HEAD(smp_alt_modules); static DEFINE_MUTEX(smp_alt); -static int smp_mode = 1; /* protected by smp_alt */ +static bool uniproc_patched = false; /* protected by smp_alt */
void __init_or_module alternatives_smp_module_add(struct module *mod, char *name, @@ -480,19 +464,18 @@ void __init_or_module alternatives_smp_m { struct smp_alt_module *smp;
- if (noreplace_smp) - return; + mutex_lock(&smp_alt); + if (!uniproc_patched) + goto unlock;
- if (smp_alt_once) { - if (boot_cpu_has(X86_FEATURE_UP)) - alternatives_smp_unlock(locks, locks_end, - text, text_end); - return; - } + if (num_possible_cpus() == 1) + /* Don't bother remembering, we'll never have to undo it. */ + goto smp_unlock;
smp = kzalloc(sizeof(*smp), GFP_KERNEL); if (NULL == smp) - return; /* we'll run the (safe but slow) SMP code then ... */ + /* we'll run the (safe but slow) SMP code then ... */ + goto unlock;
smp->mod = mod; smp->name = name; @@ -504,11 +487,10 @@ void __init_or_module alternatives_smp_m smp->locks, smp->locks_end, smp->text, smp->text_end, smp->name);
- mutex_lock(&smp_alt); list_add_tail(&smp->next, &smp_alt_modules); - if (boot_cpu_has(X86_FEATURE_UP)) - alternatives_smp_unlock(smp->locks, smp->locks_end, - smp->text, smp->text_end); +smp_unlock: + alternatives_smp_unlock(locks, locks_end, text, text_end); +unlock: mutex_unlock(&smp_alt); }
@@ -516,24 +498,18 @@ void __init_or_module alternatives_smp_m { struct smp_alt_module *item;
- if (smp_alt_once || noreplace_smp) - return; - mutex_lock(&smp_alt); list_for_each_entry(item, &smp_alt_modules, next) { if (mod != item->mod) continue; list_del(&item->next); - mutex_unlock(&smp_alt); - DPRINTK("%s\n", item->name); kfree(item); - return; + break; } mutex_unlock(&smp_alt); }
-bool skip_smp_alternatives; -void alternatives_smp_switch(int smp) +void alternatives_enable_smp(void) { struct smp_alt_module *mod;
@@ -548,34 +524,21 @@ void alternatives_smp_switch(int smp) printk("lockdep: fixing up alternatives.\n"); #endif
- if (noreplace_smp || smp_alt_once || skip_smp_alternatives) - return; - BUG_ON(!smp && (num_online_cpus() > 1)); + /* Why bother if there are no other CPUs? */ + BUG_ON(num_possible_cpus() == 1);
mutex_lock(&smp_alt);
- /* - * 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) { + if (uniproc_patched) { printk(KERN_INFO "SMP alternatives: switching to SMP code\n"); + BUG_ON(num_online_cpus() != 1); clear_cpu_cap(&boot_cpu_data, X86_FEATURE_UP); clear_cpu_cap(&cpu_data(0), X86_FEATURE_UP); list_for_each_entry(mod, &smp_alt_modules, next) alternatives_smp_lock(mod->locks, mod->locks_end, mod->text, mod->text_end); - } else { - printk(KERN_INFO "SMP alternatives: switching to UP code\n"); - set_cpu_cap(&boot_cpu_data, X86_FEATURE_UP); - set_cpu_cap(&cpu_data(0), X86_FEATURE_UP); - list_for_each_entry(mod, &smp_alt_modules, next) - alternatives_smp_unlock(mod->locks, mod->locks_end, - mod->text, mod->text_end); + uniproc_patched = false; } - smp_mode = smp; mutex_unlock(&smp_alt); }
@@ -652,40 +615,22 @@ void __init alternative_instructions(voi
apply_alternatives(__alt_instructions, __alt_instructions_end);
- /* switch to patch-once-at-boottime-only mode and free the - * tables in case we know the number of CPUs will never ever - * change */ -#ifdef CONFIG_HOTPLUG_CPU - if (num_possible_cpus() < 2) - smp_alt_once = 1; -#endif - #ifdef CONFIG_SMP - if (smp_alt_once) { - if (1 == num_possible_cpus()) { - printk(KERN_INFO "SMP alternatives: switching to UP code\n"); - set_cpu_cap(&boot_cpu_data, X86_FEATURE_UP); - set_cpu_cap(&cpu_data(0), X86_FEATURE_UP); - - alternatives_smp_unlock(__smp_locks, __smp_locks_end, - _text, _etext); - } - } else { + /* Patch to UP if other cpus not imminent. */ + if (!noreplace_smp && (num_present_cpus() == 1 || setup_max_cpus <= 1)) { + uniproc_patched = true; alternatives_smp_module_add(NULL, "core kernel", __smp_locks, __smp_locks_end, _text, _etext); - - /* Only switch to UP mode if we don't immediately boot others */ - if (num_present_cpus() == 1 || setup_max_cpus <= 1) - alternatives_smp_switch(0); } -#endif - apply_paravirt(__parainstructions, __parainstructions_end);
- if (smp_alt_once) + if (!uniproc_patched || num_possible_cpus() == 1) free_init_pages("SMP alternatives", (unsigned long)__smp_locks, (unsigned long)__smp_locks_end); +#endif + + apply_paravirt(__parainstructions, __parainstructions_end);
restart_nmi(); } --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -689,7 +689,8 @@ static int __cpuinit do_boot_cpu(int api
INIT_WORK_ONSTACK(&c_idle.work, do_fork_idle);
- alternatives_smp_switch(1); + /* Just in case we booted with a single CPU. */ + alternatives_enable_smp();
c_idle.idle = get_idle_for_cpu(cpu);
@@ -1109,20 +1110,6 @@ out: preempt_enable(); }
-void arch_disable_nonboot_cpus_begin(void) -{ - /* - * Avoid the smp alternatives switch during the disable_nonboot_cpus(). - * In the suspend path, we will be back in the SMP mode shortly anyways. - */ - skip_smp_alternatives = true; -} - -void arch_disable_nonboot_cpus_end(void) -{ - skip_smp_alternatives = false; -} - void arch_enable_nonboot_cpus_begin(void) { set_mtrr_aps_delayed_init(); @@ -1321,9 +1308,6 @@ void native_cpu_die(unsigned int cpu) if (per_cpu(cpu_state, cpu) == CPU_DEAD) { if (system_state == SYSTEM_RUNNING) pr_info("CPU %u is now offline\n", cpu); - - if (1 == num_online_cpus()) - alternatives_smp_switch(0); return; } msleep(100); --- a/arch/x86/xen/smp.c +++ b/arch/x86/xen/smp.c @@ -368,7 +368,8 @@ static int __cpuinit xen_cpu_up(unsigned return rc;
if (num_online_cpus() == 1) - alternatives_smp_switch(1); + /* Just in case we booted with a single CPU. */ + alternatives_enable_smp();
rc = xen_smp_intr_init(cpu); if (rc) @@ -414,9 +415,6 @@ static void xen_cpu_die(unsigned int cpu unbind_from_irqhandler(per_cpu(xen_callfuncsingle_irq, cpu), NULL); xen_uninit_lock_cpu(cpu); xen_teardown_timer(cpu); - - if (num_online_cpus() == 1) - alternatives_smp_switch(0); }
static void __cpuinit xen_play_dead(void) /* used only with HOTPLUG_CPU */ --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -406,14 +406,6 @@ out: #ifdef CONFIG_PM_SLEEP_SMP static cpumask_var_t frozen_cpus;
-void __weak arch_disable_nonboot_cpus_begin(void) -{ -} - -void __weak arch_disable_nonboot_cpus_end(void) -{ -} - int disable_nonboot_cpus(void) { int cpu, first_cpu, error = 0; @@ -425,7 +417,6 @@ int disable_nonboot_cpus(void) * with the userspace trying to use the CPU hotplug at the same time */ cpumask_clear(frozen_cpus); - arch_disable_nonboot_cpus_begin();
printk("Disabling non-boot CPUs ...\n"); for_each_online_cpu(cpu) { @@ -441,8 +432,6 @@ int disable_nonboot_cpus(void) } }
- arch_disable_nonboot_cpus_end(); - if (!error) { BUG_ON(num_online_cpus() > 1); /* Make sure the CPUs won't be enabled by someone else */