Re: [PATCH 1/2] workqueues: shrink cpu_populated_map when CPU dies
- From: Jarek Poplawski <jarkao2@xxxxxxxxx>
- Date: Sun, 17 Feb 2008 21:27:39 +0100
Hi Oleg,
This patch looks OK to me. But while reading this I got some doubts
in nearby places, so BTW 2 small questions:
1) ... workqueue_cpu_callback(...)
{
...
list_for_each_entry(wq, &workqueues, list) {
cwq = per_cpu_ptr(wq->cpu_wq, cpu);
switch (action) {
case CPU_UP_PREPARE:
...
It looks like not all CPU_ cases are served here: shouldn't
list_for_each_entry() be omitted for them?
2) ... __create_workqueue_key(...)
{
...
if (singlethread) {
...
} else {
get_online_cpus();
spin_lock(&workqueue_lock);
list_add(&wq->list, &workqueues);
Shouldn't this list_add() be done after all these inits below?
spin_unlock(&workqueue_lock);
for_each_possible_cpu(cpu) {
cwq = init_cpu_workqueue(wq, cpu);
...
}
...
Thanks,
Jarek P.
On Sat, Feb 16, 2008 at 08:22:59PM +0300, Oleg Nesterov wrote:
When cpu_populated_map was introduced, it was supposed that cwq->thread can--
survive after CPU_DEAD, that is why we never shrink cpu_populated_map.
This is not very nice, we can safely remove the already dead CPU from the map.
The only required change is that destroy_workqueue() must hold the hotplug lock
until it destroys all cwq->thread's, to protect the cpu_populated_map. We could
make the local copy of cpu mask and drop the lock, but sizeof(cpumask_t) may be
very large.
Also, fix the comment near queue_work(). Unless _cpu_down() happens we do
guarantee the cpu-affinity of the work_struct, and we have users which rely on
this.
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
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