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authorSteven Rostedt <srostedt@redhat.com>2009-03-24 01:10:15 -0400
committerSteven Rostedt <srostedt@redhat.com>2009-03-24 09:33:30 -0400
commit8aef2d2856158a36c295a8d1288281e4839bff13 (patch)
treeeef85397dedcad001982724e0be2da6dc089b39f /kernel/trace
parent05ce5818adee8f8efd0a5ca0d900a6789012516b (diff)
function-graph: ignore times across schedule
Impact: more accurate timings The current method of function graph tracing does not take into account the time spent when a task is not running. This shows functions that call schedule have increased costs: 3) + 18.664 us | } ------------------------------------------ 3) <idle>-0 => kblockd-123 ------------------------------------------ 3) | finish_task_switch() { 3) 1.441 us | _spin_unlock_irq(); 3) 3.966 us | } 3) ! 2959.433 us | } 3) ! 2961.465 us | } This patch uses the tracepoint in the scheduling context switch to account for time that has elapsed while a task is scheduled out. Now we see: ------------------------------------------ 3) <idle>-0 => edac-po-1067 ------------------------------------------ 3) | finish_task_switch() { 3) 0.685 us | _spin_unlock_irq(); 3) 2.331 us | } 3) + 41.439 us | } 3) + 42.663 us | } Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Diffstat (limited to 'kernel/trace')
-rw-r--r--kernel/trace/ftrace.c36
1 files changed, 36 insertions, 0 deletions
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index c81a759fbf7..0b90364d1a2 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -29,6 +29,8 @@
#include <linux/list.h>
#include <linux/hash.h>
+#include <trace/sched.h>
+
#include <asm/ftrace.h>
#include "trace.h"
@@ -2590,6 +2592,31 @@ free:
return ret;
}
+static void
+ftrace_graph_probe_sched_switch(struct rq *__rq, struct task_struct *prev,
+ struct task_struct *next)
+{
+ unsigned long long timestamp;
+ int index;
+
+ timestamp = trace_clock_local();
+
+ prev->ftrace_timestamp = timestamp;
+
+ /* only process tasks that we timestamped */
+ if (!next->ftrace_timestamp)
+ return;
+
+ /*
+ * Update all the counters in next to make up for the
+ * time next was sleeping.
+ */
+ timestamp -= next->ftrace_timestamp;
+
+ for (index = next->curr_ret_stack; index >= 0; index--)
+ next->ret_stack[index].calltime += timestamp;
+}
+
/* Allocate a return stack for each task */
static int start_graph_tracing(void)
{
@@ -2611,6 +2638,13 @@ static int start_graph_tracing(void)
ret = alloc_retstack_tasklist(ret_stack_list);
} while (ret == -EAGAIN);
+ if (!ret) {
+ ret = register_trace_sched_switch(ftrace_graph_probe_sched_switch);
+ if (ret)
+ pr_info("ftrace_graph: Couldn't activate tracepoint"
+ " probe to kernel_sched_switch\n");
+ }
+
kfree(ret_stack_list);
return ret;
}
@@ -2674,6 +2708,7 @@ void unregister_ftrace_graph(void)
mutex_lock(&ftrace_lock);
atomic_dec(&ftrace_graph_active);
+ unregister_trace_sched_switch(ftrace_graph_probe_sched_switch);
ftrace_graph_return = (trace_func_graph_ret_t)ftrace_stub;
ftrace_graph_entry = ftrace_graph_entry_stub;
ftrace_shutdown(FTRACE_STOP_FUNC_RET);
@@ -2694,6 +2729,7 @@ void ftrace_graph_init_task(struct task_struct *t)
t->curr_ret_stack = -1;
atomic_set(&t->tracing_graph_pause, 0);
atomic_set(&t->trace_overrun, 0);
+ t->ftrace_timestamp = 0;
} else
t->ret_stack = NULL;
}