netdev - RE: [PATCH] lan78xx: Protect runtime_auto check by #ifdef CONFIG

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Date:	Mon, 21 Mar 2016 15:27:00 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Woojung.Huh@...rochip.com
cc:	oneukum@...e.com, <geert@...ux-m68k.org>,
	<UNGLinuxDriver@...rochip.com>, <davem@...emloft.net>,
	<linux@...ck-us.net>, <rjw@...ysocki.net>,
	<netdev@...r.kernel.org>, <linux-usb@...r.kernel.org>,
	<linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] lan78xx: Protect runtime_auto check by #ifdef CONFIG_PM

On Mon, 21 Mar 2016 Woojung.Huh@...rochip.com wrote:

> > But this leaves open the issue that querying the device too often will
> > prevent it from going into autosuspend.  It seems to me that the best
> > way to deal with this is to make sure that the autosuspend timeout is
> > shorter than the interal between queries, not to make the querying
> > conditional on !runtime_auto.
> 
> Short autosuspend timeout can affect performance. For instance our experiments showed that
> shorter than 10sec timeout made Ethernet performance degrade because of wakeup delays.
> So, just putting shorter timeout may have some side effects.

Sure.  This just means that you need a long statistics interval --
longer than the autosuspend timeout.  That's why I suggested making the
interval adjustable.

Alternatively, you could automatically set the statistics interval to
the autosuspend timeout (or 0 if autosuspend is disabled) plus some
fixed value.

Alan Stern