linux-kernel - Re: [PATCH] serial8250: ratelimit "too much work" error

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Message-Id: <20101004164911.c8348e7e.akpm@linux-foundation.org>
Date:	Mon, 4 Oct 2010 16:49:11 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Joe Perches <joe@...ches.com>
Cc:	Daniel Drake <dsd@...top.org>, linux-serial@...r.kernel.org,
	linux-kernel@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>,
	Greg KH <greg@...ah.com>
Subject: Re: [PATCH] serial8250: ratelimit "too much work" error

On Mon, 04 Oct 2010 16:34:05 -0700
Joe Perches <joe@...ches.com> wrote:

> On Mon, 2010-10-04 at 16:11 -0700, Andrew Morton wrote:
> > On Mon, 04 Oct 2010 15:59:29 -0700
> > Joe Perches <joe@...ches.com> wrote:
> > > On Mon, 2010-10-04 at 15:21 -0700, Andrew Morton wrote:
> > > > On Mon, 04 Oct 2010 15:10:59 -0700
> > > > Joe Perches <joe@...ches.com> wrote:
> > > > > On Mon, 2010-10-04 at 15:02 -0700, Andrew Morton wrote:
> > > > > > On Mon, 4 Oct 2010 14:51:01 -0700
> > > > > > Andrew Morton <akpm@...ux-foundation.org> wrote:
> > > > > > I'll give up and pronounce that users of printk_ratelimited() need to
> > > > > > include ratelimit.h as well.
> > > > > What I suggested several months ago was to move the
> > > > > macro definitions to ratelimit.h
> > > > > http://lkml.org/lkml/2010/2/18/377
> > > > That's a bit nasty because at present ratelimit.h is purely about
> > > > ratelimiting and knowns nothing about any of its clients.  At present
> > > > it has only one client (printk), but it could have more in the future!
> > > 
> > > Look at the structure, it's very specific to
> > > message logging functionality.
> > > 
> > > struct ratelimit_state {
> > > 	spinlock_t	lock;		/* protect the state */
> > > 
> > > 	int		interval;
> > > 	int		burst;
> > > 	int		printed;
> > > 	int		missed;
> > > 	unsigned long	begin;
> > > };
> > 
> > s/printed/hit/there,fixed
> > 
> > This is at present a quite general facility.
> > 
> > > I think it's likely that the current ratelimit
> > > will not be used for any other function.
> > 
> > Filling it up with printk-specific stuff will help ensure that.
> 
> Interval too because it is in seconds and likely
> should be in timespec or jiffies.

It might need changes when adapted to additional uses.  These things
happen.

> For what other facility could you see ratelimit_state
> be used for?

Gee I dunno.  Sending occasional packets of accumulated counters up to
userspace via netlink?  Who knows, people do all sorts of things.
I bet there's code in the kernel right now which could use this.

Look at the file!  It all does one thing.  It encapsulates a single
concept.  It's simply a bad thing to add single-concept
application-specific material into that.  Layering, and all that.

> Putting the printk specific uses in the .h file
> would make sure that the users of ratelimit use
> the proper file and reduce the #include dependencies.

I know that.  It's the first thing I thought of, before deciding that
it would be a poor thing to do.
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