2006-10-30 20:48:57

by Oleg Nesterov

Subject: [PATCH] taskstats_exit_alloc: optimize/simplify

If there are no listeners, every task does unneeded kmem_cache alloc/free on
exit. We don't need listeners->sem for 'if (!list_empty())' check. Yes, we may
have a false positive, but this doesn't differ from the case when the listener
is unregistered after we drop the semaphore. So we don't need to do allocation
beforehand.

Signed-off-by: Oleg Nesterov <[email protected]>

--- STATS/kernel/taskstats.c~1_alloc 2006-10-29 18:35:40.000000000 +0300
+++ STATS/kernel/taskstats.c 2006-10-30 23:45:20.000000000 +0300
@@ -421,7 +421,6 @@ err:
void taskstats_exit_alloc(struct taskstats **ptidstats, unsigned int *mycpu)
{
struct listener_list *listeners;
- struct taskstats *tmp;
/*
* This is the cpu on which the task is exiting currently and will
* be the one for which the exit event is sent, even if the cpu
@@ -429,19 +428,11 @@ void taskstats_exit_alloc(struct tasksta
*/
*mycpu = raw_smp_processor_id();

- *ptidstats = NULL;
- tmp = kmem_cache_zalloc(taskstats_cache, SLAB_KERNEL);
- if (!tmp)
- return;
-
listeners = &per_cpu(listener_array, *mycpu);
- down_read(&listeners->sem);
- if (!list_empty(&listeners->list)) {
- *ptidstats = tmp;
- tmp = NULL;
- }
- up_read(&listeners->sem);
- kfree(tmp);
+
+ *ptidstats = NULL;
+ if (!list_empty(&listeners->list))
+ *ptidstats = kmem_cache_zalloc(taskstats_cache, SLAB_KERNEL);
}

/* Send pid data out on exit */

2006-10-31 03:04:49

by Shailabh Nagar

Subject: Re: [PATCH] taskstats_exit_alloc: optimize/simplify

Oleg Nesterov wrote:
> If there are no listeners, every task does unneeded kmem_cache alloc/free on
> exit. We don't need listeners->sem for 'if (!list_empty())' check. Yes, we may
> have a false positive, but this doesn't differ from the case when the listener
> is unregistered after we drop the semaphore. So we don't need to do allocation
> beforehand.

Sounds reasonable.


>
> Signed-off-by: Oleg Nesterov <[email protected]>

Acked-by: Shailabh Nagar <[email protected]>


>
> --- STATS/kernel/taskstats.c~1_alloc 2006-10-29 18:35:40.000000000 +0300
> +++ STATS/kernel/taskstats.c 2006-10-30 23:45:20.000000000 +0300
> @@ -421,7 +421,6 @@ err:
> void taskstats_exit_alloc(struct taskstats **ptidstats, unsigned int *mycpu)
> {
> struct listener_list *listeners;
> - struct taskstats *tmp;
> /*
> * This is the cpu on which the task is exiting currently and will
> * be the one for which the exit event is sent, even if the cpu
> @@ -429,19 +428,11 @@ void taskstats_exit_alloc(struct tasksta
> */
> *mycpu = raw_smp_processor_id();
>
> - *ptidstats = NULL;
> - tmp = kmem_cache_zalloc(taskstats_cache, SLAB_KERNEL);
> - if (!tmp)
> - return;
> -
> listeners = &per_cpu(listener_array, *mycpu);
> - down_read(&listeners->sem);
> - if (!list_empty(&listeners->list)) {
> - *ptidstats = tmp;
> - tmp = NULL;
> - }
> - up_read(&listeners->sem);
> - kfree(tmp);
> +
> + *ptidstats = NULL;
> + if (!list_empty(&listeners->list))
> + *ptidstats = kmem_cache_zalloc(taskstats_cache, SLAB_KERNEL);
> }
>
> /* Send pid data out on exit */
>