From 5d6a27d8a096868ae313f71f563b06074a7e34fe Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Sun, 14 Dec 2008 12:28:33 +0100 Subject: [PATCH] perfcounters: add context switch counter Impact: add new feature, new sw counter Add a counter that counts the number of context-switches a task is doing. Signed-off-by: Ingo Molnar --- include/linux/perf_counter.h | 4 +-- kernel/perf_counter.c | 51 ++++++++++++++++++++++++++++++++++++ 2 files changed, 53 insertions(+), 2 deletions(-) diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h index e5d25bf8f74..d2a16563415 100644 --- a/include/linux/perf_counter.h +++ b/include/linux/perf_counter.h @@ -53,8 +53,8 @@ enum hw_event_types { /* * Future software events: */ - /* PERF_COUNT_PAGE_FAULTS = -3, - PERF_COUNT_CONTEXT_SWITCHES = -4, */ + PERF_COUNT_PAGE_FAULTS = -3, + PERF_COUNT_CONTEXT_SWITCHES = -4, }; /* diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c index 1f81cde0dc4..09287091c52 100644 --- a/kernel/perf_counter.c +++ b/kernel/perf_counter.c @@ -888,6 +888,54 @@ static const struct hw_perf_counter_ops perf_ops_task_clock = { .hw_perf_counter_read = task_clock_perf_counter_read, }; +static u64 get_context_switches(void) +{ + struct task_struct *curr = current; + + return curr->nvcsw + curr->nivcsw; +} + +static void context_switches_perf_counter_update(struct perf_counter *counter) +{ + u64 prev, now; + s64 delta; + + prev = atomic64_read(&counter->hw.prev_count); + now = get_context_switches(); + + atomic64_set(&counter->hw.prev_count, now); + + delta = now - prev; + if (WARN_ON_ONCE(delta < 0)) + delta = 0; + + atomic64_add(delta, &counter->count); +} + +static void context_switches_perf_counter_read(struct perf_counter *counter) +{ + context_switches_perf_counter_update(counter); +} + +static void context_switches_perf_counter_enable(struct perf_counter *counter) +{ + /* + * ->nvcsw + curr->nivcsw is a per-task value already, + * so we dont have to clear it on switch-in. + */ +} + +static void context_switches_perf_counter_disable(struct perf_counter *counter) +{ + context_switches_perf_counter_update(counter); +} + +static const struct hw_perf_counter_ops perf_ops_context_switches = { + .hw_perf_counter_enable = context_switches_perf_counter_enable, + .hw_perf_counter_disable = context_switches_perf_counter_disable, + .hw_perf_counter_read = context_switches_perf_counter_read, +}; + static const struct hw_perf_counter_ops * sw_perf_counter_init(struct perf_counter *counter) { @@ -900,6 +948,9 @@ sw_perf_counter_init(struct perf_counter *counter) case PERF_COUNT_TASK_CLOCK: hw_ops = &perf_ops_task_clock; break; + case PERF_COUNT_CONTEXT_SWITCHES: + hw_ops = &perf_ops_context_switches; + break; default: break; } -- 2.39.5