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SubjectRe: [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U9

* Nikita Danilov <nikita@clusterfs.com> wrote:

> > > A kernel daemon that waits for some work to do is an example.
> >
> > what type of work - could you be a bit more specific?
>
> Take a loop in fs/cifs/cifsfs.c:cifs_oplock_thread() (I won't copy it
> here to avoid you all going blind). It can be recoded as
>
> while(1) {
> spin_lock(&GlobalMid_Lock);
> while (list_empty(&GlobalOplock_Q)) {
> if (kcond_timedwait(&SomeCIFSCVAR, &GlobalMid_Lock, HZ) == -EINTR) {
> spin_unlock(&GlobalMid_Lock);
> complete_and_exit(&cifs_oplock_exited, 0);
> }
> }
> oplock_item = list_entry(GlobalOplock_Q.next, struct oplock_q_entry, qhead);
> /* do stuff with oplock_item ... */
> spin_unlock(&GlobalMid_Lock);
> ....
> }

in this particular case i'd use a workqueue, which would simplify this
down to something like:

workqueue_handler()
{
spin_lock(&GlobalMid_Lock);
oplock_item = list_entry(GlobalOplock_Q.next, ...);
/* do stuff with oplock_item */
spin_unlock(&GlobalMid_Lock);
}

and instead of playing games with signals to exit the worker thread, i'd
use destroy_workqueue().

Ingo
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