Gitweb:
http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=1f2ea0837dbc263ce2a2512c4e73c83df68a6a55
Commit: 1f2ea0837dbc263ce2a2512c4e73c83df68a6a55
Parent: 7460ed2844ffad7141e30271c0c3da8336e66014
Author: Paul E. McKenney <[EMAIL PROTECTED]>
AuthorDate: Fri Feb 16 01:28:22 2007 -0800
Committer: Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Fri Feb 16 08:14:00 2007 -0800
[PATCH] posix timers: RCU optimization for clock_gettime()
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.
[EMAIL PROTECTED]: fix exit()/posix_cpu_clock_get() race spotted by Oleg]
Signed-off-by: Paul E. McKenney <[EMAIL PROTECTED]>
Signed-off-by: Ingo Molnar <[EMAIL PROTECTED]>
Cc: Thomas Gleixner <[EMAIL PROTECTED]>
Cc: john stultz <[EMAIL PROTECTED]>
Cc: Roman Zippel <[EMAIL PROTECTED]>
Cc: Oleg Nesterov <[EMAIL PROTECTED]>
Signed-off-by: Paul E. McKenney <[EMAIL PROTECTED]>
Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
---
kernel/posix-cpu-timers.c | 15 ++++++++++-----
1 files changed, 10 insertions(+), 5 deletions(-)
diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 7c3e1e6..657f776 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -304,7 +304,7 @@ int posix_cpu_clock_get(const clockid_t which_clock, struct
timespec *tp)
* 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 which_clock,
struct timespec *tp)
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)
-
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