diff --git a/arch/mips/include/asm/r4k-timer.h b/arch/mips/include/asm/r4k-timer.h index 6e7361629348..432e61dd5204 100644 --- a/arch/mips/include/asm/r4k-timer.h +++ b/arch/mips/include/asm/r4k-timer.h @@ -12,15 +12,10 @@ #ifdef CONFIG_SYNC_R4K -extern void synchronise_count_master(int cpu); extern void synchronise_count_slave(int cpu); #else -static inline void synchronise_count_master(int cpu) -{ -} - static inline void synchronise_count_slave(int cpu) { } diff --git a/arch/mips/kernel/smp.c b/arch/mips/kernel/smp.c index 0b53d35a116e..0362fc5df7b0 100644 --- a/arch/mips/kernel/smp.c +++ b/arch/mips/kernel/smp.c @@ -462,8 +462,6 @@ int __cpu_up(unsigned int cpu, struct task_struct *tidle) return -EIO; } - synchronise_count_master(cpu); - /* Wait for CPU to finish startup & mark itself online before return */ wait_for_completion(&cpu_running); return 0; diff --git a/arch/mips/kernel/sync-r4k.c b/arch/mips/kernel/sync-r4k.c index abdd7aaa3311..39156592582e 100644 --- a/arch/mips/kernel/sync-r4k.c +++ b/arch/mips/kernel/sync-r4k.c @@ -2,121 +2,244 @@ /* * Count register synchronisation. * - * All CPUs will have their count registers synchronised to the CPU0 next time - * value. This can cause a small timewarp for CPU0. All other CPU's should - * not have done anything significant (but they may have had interrupts - * enabled briefly - prom_smp_finish() should not be responsible for enabling - * interrupts...) + * Derived from arch/x86/kernel/tsc_sync.c + * Copyright (C) 2006, Red Hat, Inc., Ingo Molnar */ #include #include #include +#include +#include +#include +#include #include -#include -#include #include +#include -static unsigned int initcount = 0; -static atomic_t count_count_start = ATOMIC_INIT(0); -static atomic_t count_count_stop = ATOMIC_INIT(0); +#define COUNTON 100 +#define NR_LOOPS 3 +#define LOOP_TIMEOUT 20 -#define COUNTON 100 -#define NR_LOOPS 3 +/* + * Entry/exit counters that make sure that both CPUs + * run the measurement code at once: + */ +static atomic_t start_count; +static atomic_t stop_count; +static atomic_t test_runs; -void synchronise_count_master(int cpu) +/* + * We use a raw spinlock in this exceptional case, because + * we want to have the fastest, inlined, non-debug version + * of a critical section, to be able to prove counter time-warps: + */ +static arch_spinlock_t sync_lock = __ARCH_SPIN_LOCK_UNLOCKED; + +static uint32_t last_counter; +static uint32_t max_warp; +static int nr_warps; +static int random_warps; + +/* + * Counter warp measurement loop running on both CPUs. + */ +static uint32_t check_counter_warp(void) { - int i; - unsigned long flags; + uint32_t start, now, prev, end, cur_max_warp = 0; + int i, cur_warps = 0; - pr_info("Synchronize counters for CPU %u: ", cpu); + start = read_c0_count(); + end = start + (uint32_t) mips_hpt_frequency / 1000 * LOOP_TIMEOUT; - local_irq_save(flags); - - /* - * We loop a few times to get a primed instruction cache, - * then the last pass is more or less synchronised and - * the master and slaves each set their cycle counters to a known - * value all at once. This reduces the chance of having random offsets - * between the processors, and guarantees that the maximum - * delay between the cycle counters is never bigger than - * the latency of information-passing (cachelines) between - * two CPUs. - */ - - for (i = 0; i < NR_LOOPS; i++) { - /* slaves loop on '!= 2' */ - while (atomic_read(&count_count_start) != 1) - mb(); - atomic_set(&count_count_stop, 0); - smp_wmb(); - - /* Let the slave writes its count register */ - atomic_inc(&count_count_start); - - /* Count will be initialised to current timer */ - if (i == 1) - initcount = read_c0_count(); + for (i = 0; ; i++) { + /* + * We take the global lock, measure counter, save the + * previous counter that was measured (possibly on + * another CPU) and update the previous counter timestamp. + */ + arch_spin_lock(&sync_lock); + prev = last_counter; + now = read_c0_count(); + last_counter = now; + arch_spin_unlock(&sync_lock); /* - * Everyone initialises count in the last loop: + * Be nice every now and then (and also check whether + * measurement is done [we also insert a 10 million + * loops safety exit, so we dont lock up in case the + * counter is totally broken]): */ - if (i == NR_LOOPS-1) - write_c0_count(initcount); - + if (unlikely(!(i & 7))) { + if (now > end || i > 10000000) + break; + cpu_relax(); + touch_nmi_watchdog(); + } /* - * Wait for slave to leave the synchronization point: + * Outside the critical section we can now see whether + * we saw a time-warp of the counter going backwards: */ - while (atomic_read(&count_count_stop) != 1) - mb(); - atomic_set(&count_count_start, 0); - smp_wmb(); - atomic_inc(&count_count_stop); + if (unlikely(prev > now)) { + arch_spin_lock(&sync_lock); + max_warp = max(max_warp, prev - now); + cur_max_warp = max_warp; + /* + * Check whether this bounces back and forth. Only + * one CPU should observe time going backwards. + */ + if (cur_warps != nr_warps) + random_warps++; + nr_warps++; + cur_warps = nr_warps; + arch_spin_unlock(&sync_lock); + } } - /* Arrange for an interrupt in a short while */ - write_c0_compare(read_c0_count() + COUNTON); - - local_irq_restore(flags); - - /* - * i386 code reported the skew here, but the - * count registers were almost certainly out of sync - * so no point in alarming people - */ - pr_cont("done.\n"); + WARN(!(now-start), + "Warning: zero counter calibration delta: %d [max: %d]\n", + now-start, end-start); + return cur_max_warp; } +/* + * The freshly booted CPU initiates this via an async SMP function call. + */ +static void check_counter_sync_source(void *__cpu) +{ + unsigned int cpu = (unsigned long)__cpu; + int cpus = 2; + + atomic_set(&test_runs, NR_LOOPS); +retry: + /* Wait for the target to start. */ + while (atomic_read(&start_count) != cpus - 1) + cpu_relax(); + + /* + * Trigger the target to continue into the measurement too: + */ + atomic_inc(&start_count); + + check_counter_warp(); + + while (atomic_read(&stop_count) != cpus-1) + cpu_relax(); + + /* + * If the test was successful set the number of runs to zero and + * stop. If not, decrement the number of runs an check if we can + * retry. In case of random warps no retry is attempted. + */ + if (!nr_warps) { + atomic_set(&test_runs, 0); + + pr_info("Counter synchronization [CPU#%d -> CPU#%u]: passed\n", + smp_processor_id(), cpu); + } else if (atomic_dec_and_test(&test_runs) || random_warps) { + /* Force it to 0 if random warps brought us here */ + atomic_set(&test_runs, 0); + + pr_info("Counter synchronization [CPU#%d -> CPU#%u]:\n", + smp_processor_id(), cpu); + pr_info("Measured %d cycles counter warp between CPUs", max_warp); + if (random_warps) + pr_warn("Counter warped randomly between CPUs\n"); + } + + /* + * Reset it - just in case we boot another CPU later: + */ + atomic_set(&start_count, 0); + random_warps = 0; + nr_warps = 0; + max_warp = 0; + last_counter = 0; + + /* + * Let the target continue with the bootup: + */ + atomic_inc(&stop_count); + + /* + * Retry, if there is a chance to do so. + */ + if (atomic_read(&test_runs) > 0) + goto retry; +} + +/* + * Freshly booted CPUs call into this: + */ void synchronise_count_slave(int cpu) { - int i; - unsigned long flags; + uint32_t cur_max_warp, gbl_max_warp, count; + int cpus = 2; - local_irq_save(flags); + if (!cpu_has_counter || !mips_hpt_frequency) + return; + + /* Kick the control CPU into the counter synchronization function */ + smp_call_function_single(cpumask_first(cpu_online_mask), + check_counter_sync_source, + (unsigned long *)(unsigned long)cpu, 0); +retry: + /* + * Register this CPU's participation and wait for the + * source CPU to start the measurement: + */ + atomic_inc(&start_count); + while (atomic_read(&start_count) != cpus) + cpu_relax(); + + cur_max_warp = check_counter_warp(); /* - * Not every cpu is online at the time this gets called, - * so we first wait for the master to say everyone is ready + * Store the maximum observed warp value for a potential retry: */ + gbl_max_warp = max_warp; - for (i = 0; i < NR_LOOPS; i++) { - atomic_inc(&count_count_start); - while (atomic_read(&count_count_start) != 2) - mb(); + /* + * Ok, we are done: + */ + atomic_inc(&stop_count); - /* - * Everyone initialises count in the last loop: - */ - if (i == NR_LOOPS-1) - write_c0_count(initcount); + /* + * Wait for the source CPU to print stuff: + */ + while (atomic_read(&stop_count) != cpus) + cpu_relax(); - atomic_inc(&count_count_stop); - while (atomic_read(&count_count_stop) != 2) - mb(); + /* + * Reset it for the next sync test: + */ + atomic_set(&stop_count, 0); + + /* + * Check the number of remaining test runs. If not zero, the test + * failed and a retry with adjusted counter is possible. If zero the + * test was either successful or failed terminally. + */ + if (!atomic_read(&test_runs)) { + /* Arrange for an interrupt in a short while */ + write_c0_compare(read_c0_count() + COUNTON); + return; } - /* Arrange for an interrupt in a short while */ - write_c0_compare(read_c0_count() + COUNTON); - local_irq_restore(flags); + /* + * If the warp value of this CPU is 0, then the other CPU + * observed time going backwards so this counter was ahead and + * needs to move backwards. + */ + if (!cur_max_warp) + cur_max_warp = -gbl_max_warp; + + count = read_c0_count(); + count += cur_max_warp; + write_c0_count(count); + + pr_debug("Counter compensate: CPU%u observed %d warp\n", cpu, cur_max_warp); + + goto retry; + } -#undef NR_LOOPS