netdev - Re: [PATCH] hso.c against 2.6.27-rc5 throttle/unthrottle to prevent loss of serial data

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Message-ID: <48C13CDE.2030100@option.com>
Date:	Fri, 05 Sep 2008 16:06:22 +0200
From:	Denis Joseph Barrow <D.Barow@...ion.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	Linux USB kernel mailing list <linux-usb@...r.kernel.org>,
	Linux netdev Mailing list <netdev@...r.kernel.org>
Subject: Re: [PATCH]  hso.c against 2.6.27-rc5 throttle/unthrottle to prevent
 loss of serial data

Thanks Alan,
I didn't see that check.

I'll shave a few lines off my code & send the patch again. 

Alan Cox wrote:
> O> If my understanding of the n_tty.c code is correct it will
>> only start throttling when there is TTY_THRESHOLD_THROTTLE
>> i.e. 128 bytes left in the n_tty ring buffer this is a very low limit
>> for my driver. This means
>> that if I try to do a tty_flip_buffer_push of
>> of a tty buffer larger than 128 bytes when the threshold
>> is reached I will lose data. My urb buffers are 4k in
>> size 2 buffers of this size up to the tty layer in a row 
>> quickly I believe I'll lose data in the n_tty layer.
> 
> If there is 128 bytes left in the n_tty buffer and you push data it ends
> up in the tty_buffer queue where it will accumulate up to 64K of data
> which will be fired into the tty layer when the tty layer is willing to
> accept it (sets its receive_room).
> 
> Alan


-- 
best regards,
D.J. Barrow
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