taskstats: add context-switch counters

Make available to the user the following task and process performance
statistics:

	* Involuntary Context Switches (task_struct->nivcsw)
	* Voluntary Context Switches (task_struct->nvcsw)

Statistics information is available from:
	1. taskstats interface (Documentation/accounting/)
	2. /proc/PID/status (task only).

This data is useful for detecting hyperactivity patterns between processes.

[akpm@linux-foundation.org: cleanup]
Signed-off-by: Maxim Uvarov <muvarov@ru.mvista.com>
Cc: Shailabh Nagar <nagar@watson.ibm.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Jay Lan <jlan@engr.sgi.com>
Cc: Jonathan Lim <jlim@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 680c913575f0..9cbab7e93557 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -289,6 +289,15 @@ static inline char *task_cap(struct task_struct *p, char *buffer)
                             cap_t(p->cap_effective));
 }
 
+static inline char *task_context_switch_counts(struct task_struct *p,
+                                                char *buffer)
+{
+        return buffer + sprintf(buffer, "voluntary_ctxt_switches:\t%lu\n"
+                            "nonvoluntary_ctxt_switches:\t%lu\n",
+                            p->nvcsw,
+                            p->nivcsw);
+}
+
 int proc_pid_status(struct task_struct *task, char * buffer)
 {
         char * orig = buffer;
@@ -307,6 +316,7 @@ int proc_pid_status(struct task_struct *task, char * buffer)
 #if defined(CONFIG_S390)
         buffer = task_show_regs(task, buffer);
 #endif
+        buffer = task_context_switch_counts(task, buffer);
         return buffer - orig;
 }