linux-kernel - Re: [PATCH v1 0/3] serial: Do not count XON/XOFF in the statistics

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Date: Thu, 4 Apr 2024 18:54:38 +0300
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Jiri Slaby <jirislaby@...nel.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
	Orson Zhai <orsonzhai@...il.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Chunyan Zhang <zhang.lyra@...il.com>
Subject: Re: [PATCH v1 0/3] serial: Do not count XON/XOFF in the statistics

On Thu, Apr 04, 2024 at 07:16:55AM +0200, Jiri Slaby wrote:
> On 04. 04. 24, 0:15, Andy Shevchenko wrote:
> > Wed, Apr 03, 2024 at 05:46:14PM +0300, Andy Shevchenko kirjoitti:
> > > Some drivers count XON/XOFF in the Tx statistics, some do not.
> > > I actually a bit uncertain, but I _think_ the correct way is not
> > > to count them, hence this series.
> > 
> > Okay, it seems there are much more drivers doing that. Perhaps we need
> > to add that to the rest in this case (i.o.w. invert the series from removal
> > to addition)?
> 
> Interesting, perhaps cut & paste?
> 
> XON and XOFF are overhead IMO. So should not be counted. When they are, they
> mangle statistics as in transmitted (real) bytes per second.
> 
> How are they handled on the RX side?

It took me a while.

All serial drivers accept everything and those that care, update statics for
anything they receive. This is because of layering. The Rx XON/XOFF seems
(note I am completely unfamiliar with mysterious ways of TTY layers) to be
handled on TTY level by n_tty_receive_char_flow_ctrl(), i.o.w. we may not
skip counting it easily.

Now the question is, shall we count the control characters on output or not?
Whatever decision we made, we should document (if not yet) and align drivers
accordingly.

Another Q is what do books / other OS / projects usually do with them
WRT statistics?

If we count everything on a wire, then we must count them, otherwise
it depends on how we treat them.

P.S.
This series as is should be abandoned. But we may continue discussing topic
under this cover letter.

-- 
With Best Regards,
Andy Shevchenko