diff options
Diffstat (limited to 'arch/x86_64/kernel/smpboot.c')
| -rw-r--r-- | arch/x86_64/kernel/smpboot.c | 231 |
1 files changed, 11 insertions, 220 deletions
diff --git a/arch/x86_64/kernel/smpboot.c b/arch/x86_64/kernel/smpboot.c index daf19332f0d..35443729aad 100644 --- a/arch/x86_64/kernel/smpboot.c +++ b/arch/x86_64/kernel/smpboot.c @@ -148,217 +148,6 @@ static void __cpuinit smp_store_cpu_info(int id) print_cpu_info(c); } -/* - * New Funky TSC sync algorithm borrowed from IA64. - * Main advantage is that it doesn't reset the TSCs fully and - * in general looks more robust and it works better than my earlier - * attempts. I believe it was written by David Mosberger. Some minor - * adjustments for x86-64 by me -AK - * - * Original comment reproduced below. - * - * Synchronize TSC of the current (slave) CPU with the TSC of the - * MASTER CPU (normally the time-keeper CPU). We use a closed loop to - * eliminate the possibility of unaccounted-for errors (such as - * getting a machine check in the middle of a calibration step). The - * basic idea is for the slave to ask the master what itc value it has - * and to read its own itc before and after the master responds. Each - * iteration gives us three timestamps: - * - * slave master - * - * t0 ---\ - * ---\ - * ---> - * tm - * /--- - * /--- - * t1 <--- - * - * - * The goal is to adjust the slave's TSC such that tm falls exactly - * half-way between t0 and t1. If we achieve this, the clocks are - * synchronized provided the interconnect between the slave and the - * master is symmetric. Even if the interconnect were asymmetric, we - * would still know that the synchronization error is smaller than the - * roundtrip latency (t0 - t1). - * - * When the interconnect is quiet and symmetric, this lets us - * synchronize the TSC to within one or two cycles. However, we can - * only *guarantee* that the synchronization is accurate to within a - * round-trip time, which is typically in the range of several hundred - * cycles (e.g., ~500 cycles). In practice, this means that the TSCs - * are usually almost perfectly synchronized, but we shouldn't assume - * that the accuracy is much better than half a micro second or so. - * - * [there are other errors like the latency of RDTSC and of the - * WRMSR. These can also account to hundreds of cycles. So it's - * probably worse. It claims 153 cycles error on a dual Opteron, - * but I suspect the numbers are actually somewhat worse -AK] - */ - -#define MASTER 0 -#define SLAVE (SMP_CACHE_BYTES/8) - -/* Intentionally don't use cpu_relax() while TSC synchronization - because we don't want to go into funky power save modi or cause - hypervisors to schedule us away. Going to sleep would likely affect - latency and low latency is the primary objective here. -AK */ -#define no_cpu_relax() barrier() - -static __cpuinitdata DEFINE_SPINLOCK(tsc_sync_lock); -static volatile __cpuinitdata unsigned long go[SLAVE + 1]; -static int notscsync __cpuinitdata; - -#undef DEBUG_TSC_SYNC - -#define NUM_ROUNDS 64 /* magic value */ -#define NUM_ITERS 5 /* likewise */ - -/* Callback on boot CPU */ -static __cpuinit void sync_master(void *arg) -{ - unsigned long flags, i; - - go[MASTER] = 0; - - local_irq_save(flags); - { - for (i = 0; i < NUM_ROUNDS*NUM_ITERS; ++i) { - while (!go[MASTER]) - no_cpu_relax(); - go[MASTER] = 0; - rdtscll(go[SLAVE]); - } - } - local_irq_restore(flags); -} - -/* - * Return the number of cycles by which our tsc differs from the tsc - * on the master (time-keeper) CPU. A positive number indicates our - * tsc is ahead of the master, negative that it is behind. - */ -static inline long -get_delta(long *rt, long *master) -{ - unsigned long best_t0 = 0, best_t1 = ~0UL, best_tm = 0; - unsigned long tcenter, t0, t1, tm; - int i; - - for (i = 0; i < NUM_ITERS; ++i) { - rdtscll(t0); - go[MASTER] = 1; - while (!(tm = go[SLAVE])) - no_cpu_relax(); - go[SLAVE] = 0; - rdtscll(t1); - - if (t1 - t0 < best_t1 - best_t0) - best_t0 = t0, best_t1 = t1, best_tm = tm; - } - - *rt = best_t1 - best_t0; - *master = best_tm - best_t0; - - /* average best_t0 and best_t1 without overflow: */ - tcenter = (best_t0/2 + best_t1/2); - if (best_t0 % 2 + best_t1 % 2 == 2) - ++tcenter; - return tcenter - best_tm; -} - -static __cpuinit void sync_tsc(unsigned int master) -{ - int i, done = 0; - long delta, adj, adjust_latency = 0; - unsigned long flags, rt, master_time_stamp, bound; -#ifdef DEBUG_TSC_SYNC - static struct syncdebug { - long rt; /* roundtrip time */ - long master; /* master's timestamp */ - long diff; /* difference between midpoint and master's timestamp */ - long lat; /* estimate of tsc adjustment latency */ - } t[NUM_ROUNDS] __cpuinitdata; -#endif - - printk(KERN_INFO "CPU %d: Syncing TSC to CPU %u.\n", - smp_processor_id(), master); - - go[MASTER] = 1; - - /* It is dangerous to broadcast IPI as cpus are coming up, - * as they may not be ready to accept them. So since - * we only need to send the ipi to the boot cpu direct - * the message, and avoid the race. - */ - smp_call_function_single(master, sync_master, NULL, 1, 0); - - while (go[MASTER]) /* wait for master to be ready */ - no_cpu_relax(); - - spin_lock_irqsave(&tsc_sync_lock, flags); - { - for (i = 0; i < NUM_ROUNDS; ++i) { - delta = get_delta(&rt, &master_time_stamp); - if (delta == 0) { - done = 1; /* let's lock on to this... */ - bound = rt; - } - - if (!done) { - unsigned long t; - if (i > 0) { - adjust_latency += -delta; - adj = -delta + adjust_latency/4; - } else - adj = -delta; - - rdtscll(t); - wrmsrl(MSR_IA32_TSC, t + adj); - } -#ifdef DEBUG_TSC_SYNC - t[i].rt = rt; - t[i].master = master_time_stamp; - t[i].diff = delta; - t[i].lat = adjust_latency/4; -#endif - } - } - spin_unlock_irqrestore(&tsc_sync_lock, flags); - -#ifdef DEBUG_TSC_SYNC - for (i = 0; i < NUM_ROUNDS; ++i) - printk("rt=%5ld master=%5ld diff=%5ld adjlat=%5ld\n", - t[i].rt, t[i].master, t[i].diff, t[i].lat); -#endif - - printk(KERN_INFO - "CPU %d: synchronized TSC with CPU %u (last diff %ld cycles, " - "maxerr %lu cycles)\n", - smp_processor_id(), master, delta, rt); -} - -static void __cpuinit tsc_sync_wait(void) -{ - /* - * When the CPU has synchronized TSCs assume the BIOS - * or the hardware already synced. Otherwise we could - * mess up a possible perfect synchronization with a - * not-quite-perfect algorithm. - */ - if (notscsync || !cpu_has_tsc || !unsynchronized_tsc()) - return; - sync_tsc(0); -} - -static __init int notscsync_setup(char *s) -{ - notscsync = 1; - return 1; -} -__setup("notscsync", notscsync_setup); - static atomic_t init_deasserted __cpuinitdata; /* @@ -546,6 +335,11 @@ void __cpuinit start_secondary(void) /* otherwise gcc will move up the smp_processor_id before the cpu_init */ barrier(); + /* + * Check TSC sync first: + */ + check_tsc_sync_target(); + Dprintk("cpu %d: setting up apic clock\n", smp_processor_id()); setup_secondary_APIC_clock(); @@ -565,14 +359,6 @@ void __cpuinit start_secondary(void) */ set_cpu_sibling_map(smp_processor_id()); - /* - * Wait for TSC sync to not schedule things before. - * We still process interrupts, which could see an inconsistent - * time in that window unfortunately. - * Do this here because TSC sync has global unprotected state. - */ - tsc_sync_wait(); - /* * We need to hold call_lock, so there is no inconsistency * between the time smp_call_function() determines number of @@ -592,6 +378,7 @@ void __cpuinit start_secondary(void) cpu_set(smp_processor_id(), cpu_online_map); per_cpu(cpu_state, smp_processor_id()) = CPU_ONLINE; spin_unlock(&vector_lock); + unlock_ipi_call_lock(); cpu_idle(); @@ -1168,6 +955,11 @@ int __cpuinit __cpu_up(unsigned int cpu) /* Unleash the CPU! */ Dprintk("waiting for cpu %d\n", cpu); + /* + * Make sure and check TSC sync: + */ + check_tsc_sync_source(cpu); + while (!cpu_isset(cpu, cpu_online_map)) cpu_relax(); @@ -1190,7 +982,6 @@ void __init smp_cpus_done(unsigned int max_cpus) smp_cleanup_boot(); setup_ioapic_dest(); check_nmi_watchdog(); - time_init_gtod(); } #ifdef CONFIG_HOTPLUG_CPU |