linux-kernel - Re: [PATCH tty-next 7/7] n_tty: trace input/read flow control

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Message-ID: <529166C0.8040001@hurleysoftware.com>
Date:	Sat, 23 Nov 2013 21:38:56 -0500
From:	Peter Hurley <peter@...leysoftware.com>
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>, linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org
Subject: Re: [PATCH tty-next 7/7] n_tty: trace input/read flow control

On 11/23/2013 07:25 PM, One Thousand Gnomes wrote:
> On Fri, 22 Nov 2013 10:59:25 -0500
> Peter Hurley <peter@...leysoftware.com> wrote:
>
>> Instrument .receive_buf() and read() paths with trace_printk's
>> to aid in debugging flow control changes.
>
> tty devices have a device, we have a dev_dbg() layer. The old tty trace
> predates this but there isn't really any excuse for not using it now that
> I can see ?

I was using the ftrace facility because it has significantly less performance
impact than printk (which was an important factor while debugging flow control
problems).

That said, I could further macro-ize n_tty_trace() with selectable facility
(which would be useful when debugging problems that end in cpu death).

Regards,
Peter Hurley

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