The patch titled
posix timers: RCU optimization for clock_gettime()
has been removed from the -mm tree. Its filename was
posix-timers-rcu-optimization-for-clock_gettime.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
Subject: posix timers: RCU optimization for clock_gettime()
From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Use RCU to avoid the need to acquire tasklist_lock in the single-threaded
case of clock_gettime(). It still acquires tasklist_lock when for a
(potentially multithreaded) process. This change allows realtime
applications to frequently monitor CPU consumption of individual tasks, as
requested (and now deployed) by some off-list users.
This has been in Ingo Molnar's -rt patchset since late 2005 with no
problems reported, and tests successfully on 2.6.20-rc6, so I believe that
it is long-since ready for mainline adoption.
[paulmck@xxxxxxxxxxxxxxxxxx: fix exit()/posix_cpu_clock_get() race spotted by Oleg]
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: john stultz <johnstul@xxxxxxxxxx>
Cc: Roman Zippel <zippel@xxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/posix-cpu-timers.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)
diff -puN kernel/posix-cpu-timers.c~posix-timers-rcu-optimization-for-clock_gettime kernel/posix-cpu-timers.c
--- a/kernel/posix-cpu-timers.c~posix-timers-rcu-optimization-for-clock_gettime
+++ a/kernel/posix-cpu-timers.c
@@ -304,7 +304,7 @@ int posix_cpu_clock_get(const clockid_t
* 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)) {
@@ -312,12 +312,17 @@ int posix_cpu_clock_get(const clockid_t
error = cpu_clock_sample(which_clock,
p, &rtn);
}
- } else if (p->tgid == pid && p->signal) {
- error = cpu_clock_sample_group(which_clock,
- p, &rtn);
+ } else {
+ read_lock(&tasklist_lock);
+ if (p->tgid == pid && p->signal) {
+ error =
+ cpu_clock_sample_group(which_clock,
+ p, &rtn);
+ }
+ read_unlock(&tasklist_lock);
}
}
- read_unlock(&tasklist_lock);
+ rcu_read_unlock();
}
if (error)
_
Patches currently in -mm which might be from paulmck@xxxxxxxxxxxxxxxxxx are
origin.patch
git-block.patch
-
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
