Subject: Re: [PATCH 7/7] kfifo: add record handling functions
From: Stefani Seibold <stefani@seibold.net>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel <linux-kernel@vger.kernel.org>, Arnd Bergmann <arnd@arndb.de>,
       Andi Kleen <andi@firstfloor.org>,
       Amerigo Wang <xiyou.wangcong@gmail.com>, Joe Perches <joe@perches.com>,
       Roger Quadros <quadros.roger@gmail.com>,
       Greg Kroah-Hartman <gregkh@suse.de>,
       Mauro Carvalho Chehab <mchehab@redhat.com>
In-Reply-To: <20091123141914.e320c341.akpm@linux-foundation.org>
References: <1258704942.4426.5.camel@wall-e>
	 <1258705988.4426.22.camel@wall-e>
	 <20091123141914.e320c341.akpm@linux-foundation.org>
Content-Type: text/plain; charset="ISO-8859-15"
Date: Tue, 24 Nov 2009 07:52:06 +0100
Message-ID: <1259045526.14668.1.camel@wall-e>
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 4961
Lines: 143

Am Montag, den 23.11.2009, 14:19 -0800 schrieb Andrew Morton:
> On Fri, 20 Nov 2009 09:33:08 +0100
> Stefani Seibold <stefani@seibold.net> wrote:
> 
> >  Add kfifo_in_rec() - puts some record data into the FIFO
> >  Add kfifo_out_rec() - gets some record data from the FIFO
> >  Add kfifo_from_user_rec() - puts some data from user space into the FIFO
> >  Add kfifo_to_user_rec() - gets data from the FIFO and write it to user space
> >  Add kfifo_peek_rec() - gets the size of the next FIFO record field
> >  Add kfifo_skip_rec() - skip the next fifo out record
> >  Add kfifo_avail_rec() - determinate the number of bytes available in a record FIFO
> > 
> > Signed-off-by: Stefani Seibold <stefani@seibold.net>
> > Acked-by: Greg Kroah-Hartman <gregkh@suse.de>
> > Acked-by: Mauro Carvalho Chehab <mchehab@redhat.com>
> > Acked-by: Andi Kleen <ak@linux.intel.com>
> > ---
> >  include/linux/kfifo.h |  328 ++++++++++++++++++++++++++++++++++++++++++++++++++
> >  kernel/kfifo.c        |  286 +++++++++++++++++++++++++++++--------------
> >  2 files changed, 521 insertions(+), 93 deletions(-)
> > 
> > diff -u -N -r -p kfifo6/include/linux/kfifo.h kfifo7/include/linux/kfifo.h
> > --- kfifo6/include/linux/kfifo.h	2009-11-19 20:54:56.275420767 +0100
> > +++ kfifo7/include/linux/kfifo.h	2009-11-19 20:55:16.596339811 +0100
> > @@ -275,4 +275,332 @@ static inline unsigned int __kfifo_off(s
> >  	return off & (fifo->size - 1);
> >  }
> >  
> > +/**
> > + * __kfifo_peek_n internal helper function for determinate the length of
> > + * the next record in the fifo
> > + */
> > +static inline unsigned int __kfifo_peek_n(struct kfifo *fifo,
> > +				unsigned int recsize)
> > +{
> > +#define __KFIFO_GET(fifo, off, shift) \
> > +	((fifo)->buffer[__kfifo_off((fifo), (fifo)->out+(off))] << (shift))
> > +
> > +	unsigned int l;
> > +
> > +	l = __KFIFO_GET(fifo, 0, 0);
> > +
> > +	if (--recsize)
> > +		l |= __KFIFO_GET(fifo, 1, 8);
> > +
> > +	return l;
> > +}
> > +
> > +/**
> > + * __kfifo_poke_n internal helper function for storing the length of
> > + * the next record into the fifo
> > + */
> > +static inline void __kfifo_poke_n(struct kfifo *fifo,
> > +			unsigned int recsize, unsigned int n)
> > +{
> > +#define __KFIFO_PUT(fifo, off, val, shift) \
> > +		( \
> > +		(fifo)->buffer[__kfifo_off((fifo), (fifo)->in+(off))] = \
> > +		(unsigned char)((val) >> (shift)) \
> > +		)
> > +
> > +	__KFIFO_PUT(fifo, 0, n, 0);
> > +
> > +	if (--recsize)
> > +		__KFIFO_PUT(fifo, 1, n, 8);
> > +}
> 
> This will leave the __KFIFO_GET and __KFIFO_PUT macros defined in the
> .c files which use this header file.  That's messy and undesired, to it
> would be better to #undef these macros as early as possible.
> 
> but...

Will be fixed ...
> 
> > +static inline unsigned int __kfifo_out_rec(struct kfifo *fifo,
> > +	void *to, unsigned int n, unsigned int recsize,
> > +	unsigned int *total)
> > +{
> > +	unsigned int l;
> > +
> > +	if (!recsize) {
> > +		l = n;
> > +		if (total)
> > +			*total = l;
> > +	} else {
> > +		l = __kfifo_peek_n(fifo, recsize);
> > +		if (total)
> > +			*total = l;
> > +		if (n < l)
> > +			return l;
> > +	}
> > +
> > +	return __kfifo_out_n(fifo, to, l, recsize);
> > +}
> 
> The amount of inlining in this header is pretty wild.  These are large
> functions!  Inlining them will create a large kernel and most likely a
> slower one, due to the increased instruction cache footprint.
> 
> So please, let's see a "kfifo: uninline everything" patch?  
> 
> but...
> 
> > +/**
> > + * kfifo_out_rec - gets some record data from the FIFO
> > + * @fifo: the fifo to be used.
> > + * @to: where the data must be copied.
> > + * @n: the size of the destination buffer.
> > + * @recsize: size of record field
> > + * @total: pointer where the total number of to copied bytes should stored
> > + *
> > + * This function copies at most @n bytes from the FIFO to @to and returns the
> > + * number of bytes which cannot be copied.
> > + * A returned value greater than the @n value means that the record doesn't
> > + * fit into the @to buffer.
> > + *
> > + * Note that with only one concurrent reader and one concurrent
> > + * writer, you don't need extra locking to use these functions.
> > + */
> > +static inline __must_check unsigned int kfifo_out_rec(struct kfifo *fifo,
> > +	void *to, unsigned int n, unsigned int recsize,
> > +	unsigned int *total)
> > +
> > +{
> > +	if (!__builtin_constant_p(recsize))
> > +		return __kfifo_out_generic(fifo, to, n, recsize, total);
> > +	return __kfifo_out_rec(fifo, to, n, recsize, total);
> > +}
> 
> OK, so I see that some attention has been paid to the text footprint issue.
> 
> But how much, and was it successful?
> 

I will think about it.


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/