diff options
| -rw-r--r-- | arch/x86_64/kernel/genapic_flat.c | 96 |
1 files changed, 82 insertions, 14 deletions
diff --git a/arch/x86_64/kernel/genapic_flat.c b/arch/x86_64/kernel/genapic_flat.c index 00f3fa6df71..28284696508 100644 --- a/arch/x86_64/kernel/genapic_flat.c +++ b/arch/x86_64/kernel/genapic_flat.c @@ -20,6 +20,46 @@ #include <asm/smp.h> #include <asm/ipi.h> +/* + * The following permit choosing broadcast IPI shortcut v.s sending IPI only + * to online cpus via the send_IPI_mask varient. + * The mask version is my preferred option, since it eliminates a lot of + * other extra code that would need to be written to cleanup intrs sent + * to a CPU while offline. + * + * Sending broadcast introduces lots of trouble in CPU hotplug situations. + * These IPI's are delivered to cpu's irrespective of their offline status + * and could pickup stale intr data when these CPUS are turned online. + * + * Not using broadcast is a cleaner approach IMO, but Andi Kleen disagrees with + * the idea of not using broadcast IPI's anymore. Hence the run time check + * is introduced, on his request so we can choose an alternate mechanism. + * + * Initial wacky performance tests that collect cycle counts show + * no increase in using mask v.s broadcast version. In fact they seem + * identical in terms of cycle counts. + * + * if we need to use broadcast, we need to do the following. + * + * cli; + * hold call_lock; + * clear any pending IPI, just ack and clear all pending intr + * set cpu_online_map; + * release call_lock; + * sti; + * + * The complicated dummy irq processing shown above is not required if + * we didnt sent IPI's to wrong CPU's in the first place. + * + * - Ashok Raj <ashok.raj@intel.com> + */ +#ifdef CONFIG_HOTPLUG_CPU +#define DEFAULT_SEND_IPI (1) +#else +#define DEFAULT_SEND_IPI (0) +#endif + +static int no_broadcast=DEFAULT_SEND_IPI; static cpumask_t flat_target_cpus(void) { @@ -79,28 +119,37 @@ static void flat_send_IPI_mask(cpumask_t cpumask, int vector) local_irq_restore(flags); } -static void flat_send_IPI_allbutself(int vector) +static inline void __local_flat_send_IPI_allbutself(int vector) { - cpumask_t mask; - /* - * if there are no other CPUs in the system then - * we get an APIC send error if we try to broadcast. - * thus we have to avoid sending IPIs in this case. - */ - int this_cpu = get_cpu(); - - mask = cpu_online_map; - cpu_clear(this_cpu, mask); + if (no_broadcast) { + cpumask_t mask = cpu_online_map; + int this_cpu = get_cpu(); - if (cpus_weight(mask) >= 1) + cpu_clear(this_cpu, mask); flat_send_IPI_mask(mask, vector); + put_cpu(); + } + else + __send_IPI_shortcut(APIC_DEST_ALLBUT, vector, APIC_DEST_LOGICAL); +} - put_cpu(); +static inline void __local_flat_send_IPI_all(int vector) +{ + if (no_broadcast) + flat_send_IPI_mask(cpu_online_map, vector); + else + __send_IPI_shortcut(APIC_DEST_ALLINC, vector, APIC_DEST_LOGICAL); +} + +static void flat_send_IPI_allbutself(int vector) +{ + if (((num_online_cpus()) - 1) >= 1) + __local_flat_send_IPI_allbutself(vector); } static void flat_send_IPI_all(int vector) { - flat_send_IPI_mask(cpu_online_map, vector); + __local_flat_send_IPI_all(vector); } static int flat_apic_id_registered(void) @@ -121,6 +170,16 @@ static unsigned int phys_pkg_id(int index_msb) return ((ebx >> 24) & 0xFF) >> index_msb; } +static __init int no_ipi_broadcast(char *str) +{ + get_option(&str, &no_broadcast); + printk ("Using %s mode\n", no_broadcast ? "No IPI Broadcast" : + "IPI Broadcast"); + return 1; +} + +__setup("no_ipi_broadcast", no_ipi_broadcast); + struct genapic apic_flat = { .name = "flat", .int_delivery_mode = dest_LowestPrio, @@ -135,3 +194,12 @@ struct genapic apic_flat = { .cpu_mask_to_apicid = flat_cpu_mask_to_apicid, .phys_pkg_id = phys_pkg_id, }; + +static int __init print_ipi_mode(void) +{ + printk ("Using IPI %s mode\n", no_broadcast ? "No-Shortcut" : + "Shortcut"); + return 0; +} + +late_initcall(print_ipi_mode); |