linux-kernel - Re: [take12 3/3] kevent: Timer notifications.

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Message-ID: <20060821111848.GB8608@2ka.mipt.ru>
Date:	Mon, 21 Aug 2006 15:18:48 +0400
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Ulrich Drepper <drepper@...hat.com>,
	Andrew Morton <akpm@...l.org>, netdev <netdev@...r.kernel.org>,
	Zach Brown <zach.brown@...cle.com>, tglx@...utronix.de
Subject: Re: [take12 3/3] kevent: Timer notifications.

On Mon, Aug 21, 2006 at 12:12:39PM +0100, Christoph Hellwig (hch@...radead.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
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