The attached patch uses 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. Signed-off-by: Paul E. McKenney <[EMAIL PROTECTED]> Signed-off-by: Ingo Molnar <[EMAIL PROTECTED]> --- kernel/posix-cpu-timers.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) Index: linux/kernel/posix-cpu-timers.c =================================================================== --- linux.orig/kernel/posix-cpu-timers.c +++ linux/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)) { @@ -313,11 +313,13 @@ int posix_cpu_clock_get(const clockid_t 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) ----- End forwarded message ----- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/