From: Paul Jackson Date: Sun, 8 Jan 2006 09:02:04 +0000 (-0800) Subject: [PATCH] cpuset: skip rcu check if task is in root cpuset X-Git-Tag: v2.6.16-rc1~815 X-Git-Url: http://pilppa.com/gitweb/?a=commitdiff_plain;h=03a285f58064b8e0af08383e082e383753d9c33e;p=linux-2.6-omap-h63xx.git [PATCH] cpuset: skip rcu check if task is in root cpuset For systems that aren't using cpusets, but have them CONFIG_CPUSET enabled in their kernel (eventually this may be most distribution kernels), this patch removes even the minimal rcu_read_lock() from the memory page allocation path. Actually, it removes that rcu call for any task that is in the root cpuset (top_cpuset), which on systems not actively using cpusets, is all tasks. We don't need the rcu check for tasks in the top_cpuset, because the top_cpuset is statically allocated, so at no risk of being freed out from underneath us. Signed-off-by: Paul Jackson Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/kernel/cpuset.c b/kernel/cpuset.c index 681a5d58d40..e04c2da9dad 100644 --- a/kernel/cpuset.c +++ b/kernel/cpuset.c @@ -647,10 +647,15 @@ void cpuset_update_task_memory_state() struct task_struct *tsk = current; struct cpuset *cs; - rcu_read_lock(); - cs = rcu_dereference(tsk->cpuset); - my_cpusets_mem_gen = cs->mems_generation; - rcu_read_unlock(); + if (tsk->cpuset == &top_cpuset) { + /* Don't need rcu for top_cpuset. It's never freed. */ + my_cpusets_mem_gen = top_cpuset.mems_generation; + } else { + rcu_read_lock(); + cs = rcu_dereference(tsk->cpuset); + my_cpusets_mem_gen = cs->mems_generation; + rcu_read_unlock(); + } if (my_cpusets_mem_gen != tsk->cpuset_mems_generation) { down(&callback_sem);