linux-kernel - Re: forcedeth: option to disable 100Hz timer (try 2)

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Message-ID: <20080911081919.56560a8a@laska>
Date:	Thu, 11 Sep 2008 08:19:19 +0400
From:	Mikhail Kshevetskiy <mikhail.kshevetskiy@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Robert Hancock <hancockr@...w.ca>, linux-kernel@...r.kernel.org,
	aabdulla@...dia.com, jgarzik@...ox.com
Subject: Re: forcedeth: option to disable 100Hz timer (try 2)

On Wed, 10 Sep 2008 17:36:30 -0700
Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Wed, 10 Sep 2008 18:18:20 -0600
> Robert Hancock <hancockr@...w.ca> wrote:
> 
> > Andrew Morton wrote:
> > > On Tue, 9 Sep 2008 23:34:35 +0400
> > > Mikhail Kshevetskiy <mikhail.kshevetskiy@...il.com> wrote:
> > > 
> > >> On some hardware no TX done interrupts are generated, thus special
> > >> 100Hz timer interrupt is required to handle this situation properly.
> > >> Other device do not require that timer interrupt feature. 
> > >>
> > >> Forcedeth has a DEV_NEED_TIMERIRQ flag to mark the broken devices.
> > >> Unfortunately, nobody know the actual list of broken devices, so all
> > >> device has this flag on. Other problem, this flag is not user visible,
> > >> so the kernel recompilation is required to disable timer interrupts and
> > >> test a device.
> > >>
> > >> This patch add a "disable_timerirq" option to disable interrupt 
> > >> timer mentioned above. This may be extremely useful for laptop users.
> > > 
> > > Why do you feel that the timer-based completions need to be disabled? 
> > > Is it causing some problem?
> > 
> > 100 unnecessary CPU wakeups per second imposes some power usage cost, 
> > especially on laptops with CPU C-states..
> 
> Is that the only reason for the change?  We still don't know...
> 
> 
> 
> Anyway, it's certainly _sufficient_ reason, however the implementation
> is pretty sad - most people won't even know that the option exists so
> they'll continue to chew more power than they need to.
> 
> How do we fix this?  Perhaps disable the timer by default, then wait
> for the first tx timeout and then enable the timer at that stage, while
> printing a message saying "add module option <foo> to prevent this
> once-off timeout from happening"?

I'll try this
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