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

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Date:	Thu, 31 Dec 2009 01:33:29 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Stefani Seibold <stefani@...bold.net>
Cc:	Andy Walls <awalls@...ix.net>,
	Vikram Dhillon <dhillonv10@...il.com>,
	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 Thu, Dec 31, 2009 at 09:59:51AM +0100, Stefani Seibold wrote:
> Am Mittwoch, den 30.12.2009, 23:35 -0800 schrieb Dmitry Torokhov:
> 
> > > 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).
> > 
> > Hmm, so there you have a local buffer that you fill by reading from the
> > device word by word, then you copy that data over into fifo and then you
> > upper layer again fetches that fifo as byte stream...
> > 
> > I'd probably simply move the processing that you are doing in
> > cx23888_ir_rx_read() into cx23888_ir_irq_handler() (since it is very
> > simple) and then used kfifo in simple byte mode (since that is what
> > upper layer seem to expect).
> > 
> 
> Why using byte mode? He can use any type he like, the new macro based
> implementation is record based! And a record can be a byte or any other
> data type. Why do you discuss about code you didn't understand and want
> not try? Why to discuss and waste time about less than 400 bytes of
> library code? Terminate this useless discussion.
> 

Yes, indeed. 

-- 
Dmitry
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