linux-kernel - Re: Regression: ftdi_sio is slow (since Wed Oct 10 15:05:06 2012)

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Message-ID: <51850295.6020601@list.ru>
Date:	Sat, 04 May 2013 16:44:05 +0400
From:	Stas Sergeev <stsp@...t.ru>
To:	Johan Hovold <jhovold@...il.com>
CC:	Greg KH <gregkh@...uxfoundation.org>,
	Jarkko Huijts <jarkko.huijts@...il.com>,
	Alan Cox <alan@...ux.intel.com>, linux-usb@...r.kernel.org,
	linux-serial@...r.kernel.org,
	Linux kernel <linux-kernel@...r.kernel.org>,
	Caylan Van Larson <i@...lan.net>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: Regression: ftdi_sio is slow (since Wed Oct 10 15:05:06 2012)

04.05.2013 15:15, Johan Hovold пишет:
> The query takes longer than the transmit at decent baudrates (>=38k)
> and under the assumption that flow control isn't causing any delays.
>
> But you do have a point, and I have been meaning to look into whether
> the added overhead of checking the hardware buffers could be mitigated
> by adding wait_until_sent support to usb-serial. This way the we would
> only query the hardware buffers on tty_wait_until_sent (e.g. at close)
> and select and TIOCMOUTQ would not suffer. This is also the way things
> are handled in serial_core.
Thanks for taking a look.
Indeed, it seems .wait_until_sent is the best candidate for that
kind of things, and the patch in question would even match its
description be it using .wait_until_sent and not .chars_in_buffer.
Please count on testing your patches here when they are ready.
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