The patch titled
ptrace: don't run write_lock(tasklist_lock) if the parent doesn't ptrace other processes
has been added to the -mm tree. Its filename is
ptrace-dont-run-write_locktasklist_lock-if-the-parent-doesnt-ptrace-other-processes.patch
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------------------------------------------------------
Subject: ptrace: don't run write_lock(tasklist_lock) if the parent doesn't ptrace other processes
From: "Zhang, Yanmin" <yanmin_zhang@xxxxxxxxxxxxxxx>
We run some sub-cases (fork, exec, pipe, tcp, udp) of aim7 on 8-socket
machine. Perf shows write_lock_irq(&tasklist_lock) consumes more than 50%
cpu time.
One hot caller is exit_ptrace. If the exiting process doesn't ptrace
other processes, kernel needn't apply for the write lock on tasklist_lock.
With this patch against kernel 2.6.35-rc5, we get more than 10% result
improvement.
Signed-off-by: Zhang Yanmin <yanmin_zhang@xxxxxxxxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Andi Kleen <andi@xxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/ptrace.c | 3 +++
1 file changed, 3 insertions(+)
diff -puN kernel/ptrace.c~ptrace-dont-run-write_locktasklist_lock-if-the-parent-doesnt-ptrace-other-processes kernel/ptrace.c
--- a/kernel/ptrace.c~ptrace-dont-run-write_locktasklist_lock-if-the-parent-doesnt-ptrace-other-processes
+++ a/kernel/ptrace.c
@@ -331,6 +331,9 @@ void exit_ptrace(struct task_struct *tra
struct task_struct *p, *n;
LIST_HEAD(ptrace_dead);
+ if (list_empty(&tracer->ptraced))
+ return;
+
write_lock_irq(&tasklist_lock);
list_for_each_entry_safe(p, n, &tracer->ptraced, ptrace_entry) {
if (__ptrace_detach(tracer, p))
_
Patches currently in -mm which might be from yanmin_zhang@xxxxxxxxxxxxxxx are
ptrace-dont-run-write_locktasklist_lock-if-the-parent-doesnt-ptrace-other-processes.patch
linux-next.patch
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