linux-kernel - Re: [PATCH v2 6/9] n_tty: Process echoes in blocks

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Date:	Wed, 24 Jul 2013 21:33:04 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
	Jiri Slaby <jslaby@...e.cz>
Subject: Re: [PATCH v2 6/9] n_tty: Process echoes in blocks

On 07/23/2013 07:53 PM, Greg Kroah-Hartman wrote:
> On Sat, Jun 15, 2013 at 10:04:26AM -0400, Peter Hurley wrote:
>> Byte-by-byte echo output is painfully slow, requiring a lock/unlock
>> cycle for every input byte.
>>
>> Instead, perform the echo output in blocks of 256 characters, and
>> at least once per flip buffer receive. Enough space is reserved in
>> the echo buffer to guarantee a full block can be saved without
>> overrunning the echo output. Overrun is prevented by discarding
>> the oldest echoes until enough space exists in the echo buffer
>> to receive at least a full block of new echoes.
>
> I'm a bit worried about this, I wonder if anything is expecting the
> echos to not come in "bursts" like this, but I really can't think of why
> they would want that.

The block size for echoes is trivially settable so if you'd prefer a
smaller value than every 256 chars, I could send a patch for a value
you are more comfortable with - 64 chars, 32 chars, whatever.

I picked that value from casual performance testing and that it
coincides with the smallest possible flip buffer; ie., echo blocks are
retired at the same rate as flip buffers when receiving is not
saturated.

> So let's apply it and see what breaks!  :)

I'm ready :)

Regards,
Peter Hurley

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