Hi All,
I appreciate if somebody can tell me why spinlock and semaphore are utilized
to protect work queue in drbd worker thread. I have some performance issue
with regard to the use of this semaphore. Specifically, down_interruptible
takes too long to be waked up. Here is the detail:
In drbd_worker.c, function int drbd_worker(struct drbd_thread *thi).
int drbd_worker(struct drbd_thread *thi)
{
....
if (down_trylock(&mdev->data.work.s)) {
mutex_lock(&mdev->data.mutex);
if (mdev->data.socket && !mdev->net_conf->no_cork)
drbd_tcp_uncork(mdev->data.socket);
mutex_unlock(&mdev->data.mutex);
intr = down_interruptible(&mdev->data.work.s);
mutex_lock(&mdev->data.mutex);
if (mdev->data.socket && !mdev->net_conf->no_cork)
drbd_tcp_cork(mdev->data.socket);
mutex_unlock(&mdev->data.mutex);
}
....
w = NULL;
spin_lock_irq(&mdev->data.work.q_lock);
ERR_IF(list_empty(&mdev->data.work.q)) {
/* something terribly wrong in our logic.
* we were able to down() the semaphore,
* but the list is empty... doh.
*
* what is the best thing to do now?
* try again from scratch, restarting the receiver,
* asender, whatnot? could break even more ugly,
* e.g. when we are primary, but no good local data.
*
* I'll try to get away just starting over this
loop.
*/
spin_unlock_irq(&mdev->data.work.q_lock);
continue;
}
...
}
I tried to get rid of semaphore in above as well as in drbd_queue_work in
drbd_ini.h. Somehow, the code breaks ugly. I guess I still don`t get the
design rational here. Any help is appreciated.
Thanks
Ben
Commit yourself to constant self-improvement
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