Date: Tue, 8 Aug 2006 08:24:10 -0400 (EDT)
From: Steven Rostedt <rostedt@goodmis.org>
To: David Miller <davem@davemloft.net>
cc: tytso@mit.edu, mchan@broadcom.com, herbert@gondor.apana.org.au,
       linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
       tglx@linutronix.de, mingo@elte.hu
Subject: Re: [PATCH -rt DO NOT APPLY] Fix for tg3 networking lockup
In-Reply-To: <20060806.231846.71090637.davem@davemloft.net>
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On Sun, 6 Aug 2006, David Miller wrote:

> From: Steven Rostedt <rostedt@goodmis.org>
> Date: Mon, 7 Aug 2006 01:34:56 -0400 (EDT)
>
> > My suggestion would be to separate that tg3_timer into 4 different
> > timers, which is what it actually looks like.
>
> Timers have non-trivial cost.  It's cheaper to have one and
> vector off to the necessary operations each tick internalls.
>
> That's why it's implemented as one timer.
>

hrtimers don't have the cost of a normal timer. And that's why I suggested
to convert them.  There's a much bigger cost in a single timer that always
times out than 3 hrtimers.  hrtimers are expected to timeout, but timers
are not.

Of the 4 timers, only one is a timeout. The other three expire every time,
forcing the timer wheel into effect.  Even though it's one timer
implementing 4, it's expensive to use it as a watchdog.

-- Steve

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