Hello!
The attached patch uses RCU to avoid the need to acquire tasklist_lock
in the single-thread case of clock_gettime(). Still acquires tasklist_lock
when asking for the time of a (potentially multithreaded) process.
Experimental, has been touch-tested on x86 and POWER. Requires RCU on
task_struct. Further more focused testing in progress.
Thoughts? (Why? Some off-list users want to be able to monitor CPU
consumption of specific threads. They need to do so quite frequently,
so acquiring tasklist_lock is inappropriate.)
Thanx, Paul
diff -urpNa -X dontdiff linux-2.6.14-rc5-rt2/kernel/posix-cpu-timers.c linux-2.6.14-rc5-rt2-RCUgettime/kernel/posix-cpu-timers.c
--- linux-2.6.14-rc5-rt2/kernel/posix-cpu-timers.c 2005-10-22 14:45:56.000000000 -0700
+++ linux-2.6.14-rc5-rt2-RCUgettime/kernel/posix-cpu-timers.c 2005-10-22 15:44:27.000000000 -0700
@@ -302,7 +302,7 @@ int posix_cpu_clock_get(clockid_t which_
* should be able to see it.
*/
struct task_struct *p;
- read_lock(&tasklist_lock);
+ rcu_read_lock();
p = find_task_by_pid(pid);
if (p) {
if (CPUCLOCK_PERTHREAD(which_clock)) {
@@ -311,11 +311,13 @@ int posix_cpu_clock_get(clockid_t which_
p, &rtn);
}
} else if (p->tgid == pid && p->signal) {
+ read_lock(&tasklist_lock);
error = cpu_clock_sample_group(which_clock,
p, &rtn);
+ read_unlock(&tasklist_lock);
}
}
- read_unlock(&tasklist_lock);
+ rcu_read_unlock();
}
if (error)
-
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