linux-kernel - Re: [PATCH] [0/6] kfifo fixes/improvements

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Date:	Wed, 30 Dec 2009 12:29:12 -0500
From:	Andy Walls <awalls@...ix.net>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Vikram Dhillon <dhillonv10@...il.com>,
	Stefani Seibold <stefani@...bold.net>,
	Andi Kleen <andi@...stfloor.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...l.org" <akpm@...l.org>
Subject: Re: [PATCH] [0/6] kfifo fixes/improvements

On Tue, 2009-12-29 at 18:08 -0800, Dmitry Torokhov wrote:
> A: http://en.wikipedia.org/wiki/Top_post
> Q: Were do I find info about this thing called top-posting?
> A: Because it messes up the order in which people normally read text.
> Q: Why is top-posting such a bad thing?
> 
> On Tue, Dec 29, 2009 at 08:18:50PM -0500, Vikram Dhillon wrote:
> > IMHO you can process elements rather than bytes, which is a good
> > improvement, but then again its my opinion, if others don't like it
> > then we can always change it :D
> 
> Right, I was not arguing against having a record-oriented interface, I
> was questioning the utility of processing several records at a time.
> Kfifo users that I have seen so far were working in a record-at-a-time
> mode.

I have a use case in linux/drivers/media/video/cx23885/cx23888-ir.c
right now.

I have a hardware fifo that can hold up to 8 values, 17 bits each - and
the high bit of the value is a flag indicating if more data is in the
hardware fifo.

The hardware fifo watermark for generating an interrupt is 4 or more
values in the hardware fifo.

I use a kfifo that needs to be protected with a spinlock.

It in much better in the IRQ context to drain the hardware fifo and then
put records in the kfifo all at once (or at least in groups of 8 or less
but usually greater than 1).

Regards,
Andy

> Thanks.


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