Avoid taking the tasklist_lock in sys_times if the process is
single threaded. In a NUMA system taking the tasklist_lock may
cause a bouncing cacheline if multiple independent processes
continually call sys_times to measure their performance.
Patch against 2.6.12-rc4
Signed-off-by: Christoph Lameter <[email protected]>
Signed-off-by: Shai Fultheim <[email protected]>
Index: linux-2.6.11/kernel/sys.c
===================================================================
--- linux-2.6.11.orig/kernel/sys.c 2005-05-17 12:46:12.000000000 -0700
+++ linux-2.6.11/kernel/sys.c 2005-05-17 12:59:36.000000000 -0700
@@ -894,35 +894,49 @@ asmlinkage long sys_times(struct tms __u
*/
if (tbuf) {
struct tms tmp;
- struct task_struct *tsk = current;
- struct task_struct *t;
cputime_t utime, stime, cutime, cstime;
- read_lock(&tasklist_lock);
- utime = tsk->signal->utime;
- stime = tsk->signal->stime;
- t = tsk;
- do {
- utime = cputime_add(utime, t->utime);
- stime = cputime_add(stime, t->stime);
- t = next_thread(t);
- } while (t != tsk);
-
- /*
- * While we have tasklist_lock read-locked, no dying thread
- * can be updating current->signal->[us]time. Instead,
- * we got their counts included in the live thread loop.
- * However, another thread can come in right now and
- * do a wait call that updates current->signal->c[us]time.
- * To make sure we always see that pair updated atomically,
- * we take the siglock around fetching them.
- */
- spin_lock_irq(&tsk->sighand->siglock);
- cutime = tsk->signal->cutime;
- cstime = tsk->signal->cstime;
- spin_unlock_irq(&tsk->sighand->siglock);
- read_unlock(&tasklist_lock);
+ if (current == next_thread(current)) {
+ /*
+ * Single thread case. We do not need to scan the tasklist
+ * and thus can avoid the read_lock(&task_list_lock). We
+ * also do not need to take the siglock since we
+ * are the only thread in this process
+ */
+ utime = cputime_add(current->signal->utime, current->utime);
+ stime = cputime_add(current->signal->utime, current->stime);
+ cutime = current->signal->cutime;
+ cstime = current->signal->cstime;
+ } else {
+ /* Process with multiple threads */
+ struct task_struct *tsk = current;
+ struct task_struct *t;
+
+ read_lock(&tasklist_lock);
+ utime = tsk->signal->utime;
+ stime = tsk->signal->stime;
+ t = tsk;
+ do {
+ utime = cputime_add(utime, t->utime);
+ stime = cputime_add(stime, t->stime);
+ t = next_thread(t);
+ } while (t != tsk);
+ /*
+ * While we have tasklist_lock read-locked, no dying thread
+ * can be updating current->signal->[us]time. Instead,
+ * we got their counts included in the live thread loop.
+ * However, another thread can come in right now and
+ * do a wait call that updates current->signal->c[us]time.
+ * To make sure we always see that pair updated atomically,
+ * we take the siglock around fetching them.
+ */
+ spin_lock_irq(&tsk->sighand->siglock);
+ cutime = tsk->signal->cutime;
+ cstime = tsk->signal->cstime;
+ spin_unlock_irq(&tsk->sighand->siglock);
+ read_unlock(&tasklist_lock);
+ }
tmp.tms_utime = cputime_to_clock_t(utime);
tmp.tms_stime = cputime_to_clock_t(stime);
tmp.tms_cutime = cputime_to_clock_t(cutime);
-
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