Re: [take12 3/3] kevent: Timer notifications.

Evgeniy Polyakov
2006-08-21T11:20:34Z

On Mon, Aug 21, 2006 at 12:12:39PM +0100, Christoph Hellwig (hch@infradead.org) wrote:
> On Mon, Aug 21, 2006 at 02:19:49PM +0400, Evgeniy Polyakov wrote:
> >
> >
> > Timer notifications.
> >
> > Timer notifications can be used for fine grained per-process time
> > management, since interval timers are very inconvenient to use,
> > and they are limited.
>
> Shouldn't this at leat use a hrtimer?

Not everymachine has them and getting into account possibility that
userspace can be scheduled away, it will be overkill.

> > new file mode 100644
> > index 0000000..5217cd1
> > --- /dev/null
> > +++ b/kernel/kevent/kevent_timer.c
> > @@ -0,0 +1,107 @@
> > +/*
> > + * kevent_timer.c
>
> You still include those sill filename ontop of file comments..

Sorry, it looks like I updated not every file.

> > +static struct lock_class_key kevent_timer_key;
> > +
> > +static int kevent_timer_enqueue(struct kevent *k)
> > +{
> > + int err;
> > + struct kevent_timer *t;
> > +
> > + t = kmalloc(sizeof(struct kevent_timer), GFP_KERNEL);
> > + if (!t)
> > + return -ENOMEM;
> > +
> > + setup_timer(&t->ktimer, &kevent_timer_func, (unsigned long)k);
> > +
> > + err = kevent_storage_init(&t->ktimer, &t->ktimer_storage);
> > + if (err)
> > + goto err_out_free;
> > + lockdep_set_class(&t->ktimer_storage.lock, &kevent_timer_key);
>
> When looking at the kevent_storage_init callers most need to do
> those lockdep_set_class class. Shouldn't kevent_storage_init just
> get a "struct lock_class_key *" argument?

It will not work, since inode is used for both socket and inode
notifications (to save some space in struct sock), lockdep initalization
is performed on the highest level, so I put it alone.

> > +static int kevent_timer_callback(struct kevent *k)
> > +{
> > + k->event.ret_data[0] = (__u32)jiffies;
>
> This is returned to userspace, isn't it? raw jiffies should never be
> user-visible. Please convert this to an unit that actually makes sense
> for userspace (probably nanoseconds)

It is just to show something, my userspace application just prints it to
stdout to show kernelspace difference between events.
Andrew pointed to it too, I think it is easier to just remove this string.

> > +static int __init kevent_init_timer(void)
> > +{
> > + struct kevent_callbacks tc = {
> > + .callback = &kevent_timer_callback,
> > + .enqueue = &kevent_timer_enqueue,
> > + .dequeue = &kevent_timer_dequeue};
>
> I think this should be static, and the normal style to write it would be:
>
> static struct kevent_callbacks tc = {
> .callback = kevent_timer_callback,
> .enqueue = kevent_timer_enqueue,
> .dequeue = kevent_timer_dequeue,
> };
>
> also please consider makring all the kevent_callbacks structs const
> to avoid false cacheline sharing and accidental modification, similar
> to what we did to various other operation vectors.

Ok.

--
Evgeniy Polyakov