netdev - RE: printk_ratelimit and net_ratelimit conflict and tunable behavior

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Date:	Thu, 28 Feb 2008 10:19:02 -0600
From:	"Hawkes Steve-FSH016" <Steve.Hawkes@...orola.com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	<davem@...emloft.net>, <joe@...ches.com>,
	<linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>
Subject: RE: printk_ratelimit and net_ratelimit conflict and tunable behavior

Andrew Morton wrote:

> This patch causes a large and nasty reject.
> Probably because you patched 2.6.24.  We're developing 2.6.25 now, and
> the difference between the two is very large inded.  Please raise
patches
> against Linus's latest tree?

Will do. I'm learning the process. I assume Linus's latest tree is the
one
listed as the latest prepatch for the stable Linux kernel tree.

Andrew Morton wrote:

> > struct printk_ratelimit_state {
> > +	unsigned long toks;
> > +	unsigned long last_jiffies;
> > +	int missed;
> > +	int limit_jiffies;
> > +	int limit_burst;
> > +	char const *facility;
> > +};
> 
> I find that the best-value comments one can add to kernel code are to
the
> members of structures.  If the reader understands what all the fields
do, the
> code becomes simple to follow.

Agreed. Although the current kernel source doesn't document these
attributes, there's no reason I couldn't add documentation for them.

Andrew Morton wrote:

> >  int net_ratelimit(void)
> >  {
> > -	return __printk_ratelimit(net_msg_cost, net_msg_burst);
> > +	static struct printk_ratelimit_state limit_state = {
> > +		.toks          = 10 * 5 * HZ,
> > +		.last_jiffies  = 0,
> > +		.missed        = 0,
> > +		.limit_jiffies = 5 * HZ,
> > +		.limit_burst   = 10,
> > +		.facility      = "net"
> > +	};
> > +
> > +	return __printk_ratelimit(net_msg_cost, net_msg_burst,
&limit_state);
> 
> I don't get it.  There's one instance of limit_state, kernel-wide, and
> __printk_ratelimit() modifies it.  What prevents one CPU's activities
from
> interfering with a second CPU's activities?

The state is protected by the spinlock in __printk_ratelimit, like it is
in
the current kernel. Am I missing something?
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