From 33266bcd74a29c5a507380f626daf9a1fd2efbdf Mon Sep 17 00:00:00 2001 From: Christoph Lameter Date: Fri, 3 Jan 2014 14:10:27 +1100 Subject: [PATCH] kmod: run usermodehelpers only on cpus allowed for kthreadd V2 usermodehelper() threads can currently run on all processors. This is an issue for low latency cores. Spawnig a new thread causes cpu holdoffs in the range of hundreds of microseconds to a few milliseconds. Not good for cores on which processes run that need to react as fast as possible. kthreadd threads can be restricted using taskset to a limited set of processors. Then the kernel thread pool will not fork processes on those anymore thereby protecting those processors from additional latencies. Make usermodehelper() threads obey the limitations that kthreadd is restricted to. Kthreadd is not the parent of usermodehelper threads so we need to explicitly get the allowed processors for kthreadd. Before this patch there is no way to limit the cpus that usermodehelper can run on since the affinity is set when the thread is spawned to all processors. Signed-off-by: Christoph Lameter Cc: Frederic Weisbecker Cc: Mike Galbraith Cc: Thomas Gleixner Cc: Gilad Ben-Yossef Cc: "Paul E. McKenney" Cc: Mike Frysinger Cc: Tejun Heo Cc: Rusty Russell Signed-off-by: Andrew Morton --- include/linux/kthread.h | 1 + kernel/kmod.c | 10 ++++++++-- kernel/kthread.c | 9 +++++++++ 3 files changed, 18 insertions(+), 2 deletions(-) diff --git a/include/linux/kthread.h b/include/linux/kthread.h index 7dcef3317689..50050ae17b00 100644 --- a/include/linux/kthread.h +++ b/include/linux/kthread.h @@ -51,6 +51,7 @@ void kthread_parkme(void); int kthreadd(void *unused); extern struct task_struct *kthreadd_task; extern int tsk_fork_get_node(struct task_struct *tsk); +void set_kthreadd_affinity(void); /* * Simple work processor based on kthread. diff --git a/kernel/kmod.c b/kernel/kmod.c index b086006c59e7..bb35c99fe95c 100644 --- a/kernel/kmod.c +++ b/kernel/kmod.c @@ -40,6 +40,7 @@ #include #include #include +#include #include @@ -209,8 +210,13 @@ static int ____call_usermodehelper(void *data) flush_signal_handlers(current, 1); spin_unlock_irq(¤t->sighand->siglock); - /* We can run anywhere, unlike our parent keventd(). */ - set_cpus_allowed_ptr(current, cpu_all_mask); + /* + * Kthreadd can be restricted to a set of processors if the user wants to + * protect other processors from OS latencies. If that has happened then + * we do not want to disturb the other processors here either so we start + * the usermode helper threads only on the processors allowed for kthreadd. + */ + set_kthreadd_affinity(); /* * Our parent is keventd, which runs with elevated scheduling priority. diff --git a/kernel/kthread.c b/kernel/kthread.c index b5ae3ee860a9..fc0d0d3e6043 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -136,6 +136,15 @@ void *kthread_data(struct task_struct *task) return to_kthread(task)->data; } +/* + * Set the affinity of the calling task to be the same + * as the kthreadd affinities. + */ +void set_kthreadd_affinity(void) +{ + set_cpus_allowed(current, kthreadd_task->cpus_allowed); +} + /** * probe_kthread_data - speculative version of kthread_data() * @task: possible kthread task in question -- 2.39.5