From: Paul Mackerras Impact: cooperate with oprofile At present, on PowerPC, if you have perf_counters compiled in, oprofile doesn't work. There is code to allow the PMU to be shared between competing subsystems, such as perf_counters and oprofile, but currently the perf_counter subsystem reserves the PMU for itself at boot time, and never releases it. This makes perf_counter play nicely with oprofile. Now we keep a count of how many perf_counter instances are counting hardware events, and reserve the PMU when that count becomes non-zero, and release the PMU when that count becomes zero. This means that it is possible to have perf_counters compiled in and still use oprofile, as long as there are no hardware perf_counters active. This also means that if oprofile is active, sys_perf_counter_open will fail if the hw_event specifies a hardware event. To avoid races with other tasks creating and destroying perf_counters, we use a mutex. We use atomic_inc_not_zero and atomic_add_unless to avoid having to take the mutex unless there is a possibility of the count going between 0 and 1. Signed-off-by: Paul Mackerras Signed-off-by: Peter Zijlstra --- arch/powerpc/kernel/perf_counter.c | 47 +++++++++++++++++++++++++++++++++---- 1 file changed, 42 insertions(+), 5 deletions(-) Index: linux-2.6/arch/powerpc/kernel/perf_counter.c =================================================================== --- linux-2.6.orig/arch/powerpc/kernel/perf_counter.c +++ linux-2.6/arch/powerpc/kernel/perf_counter.c @@ -41,6 +41,8 @@ struct power_pmu *ppmu; */ static unsigned int freeze_counters_kernel = MMCR0_FCS; +static void perf_counter_interrupt(struct pt_regs *regs); + void perf_counter_print_debug(void) { } @@ -594,6 +596,24 @@ struct hw_perf_counter_ops power_perf_op .read = power_perf_read }; +/* Number of perf_counters counting hardware events */ +static atomic_t num_counters; +/* Used to avoid races in calling reserve/release_pmc_hardware */ +static DEFINE_MUTEX(pmc_reserve_mutex); + +/* + * Release the PMU if this is the last perf_counter. + */ +static void hw_perf_counter_destroy(struct perf_counter *counter) +{ + if (!atomic_add_unless(&num_counters, -1, 1)) { + mutex_lock(&pmc_reserve_mutex); + if (atomic_dec_return(&num_counters) == 0) + release_pmc_hardware(); + mutex_unlock(&pmc_reserve_mutex); + } +} + const struct hw_perf_counter_ops * hw_perf_counter_init(struct perf_counter *counter) { @@ -601,6 +621,7 @@ hw_perf_counter_init(struct perf_counter struct perf_counter *ctrs[MAX_HWCOUNTERS]; unsigned int events[MAX_HWCOUNTERS]; int n; + int err; if (!ppmu) return NULL; @@ -646,6 +667,27 @@ hw_perf_counter_init(struct perf_counter counter->hw.config = events[n]; atomic64_set(&counter->hw.period_left, counter->hw_event.irq_period); + + /* + * See if we need to reserve the PMU. + * If no counters are currently in use, then we have to take a + * mutex to ensure that we don't race with another task doing + * reserve_pmc_hardware or release_pmc_hardware. + */ + err = 0; + if (!atomic_inc_not_zero(&num_counters)) { + mutex_lock(&pmc_reserve_mutex); + if (atomic_read(&num_counters) == 0 && + reserve_pmc_hardware(perf_counter_interrupt)) + err = -EBUSY; + else + atomic_inc(&num_counters); + mutex_unlock(&pmc_reserve_mutex); + } + counter->destroy = hw_perf_counter_destroy; + + if (err) + return NULL; return &power_perf_ops; } @@ -756,11 +798,6 @@ static int init_perf_counters(void) { unsigned long pvr; - if (reserve_pmc_hardware(perf_counter_interrupt)) { - printk(KERN_ERR "Couldn't init performance monitor subsystem\n"); - return -EBUSY; - } - /* XXX should get this from cputable */ pvr = mfspr(SPRN_PVR); switch (PVR_VER(pvr)) { -- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/