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SubjectRe: [PATCH 3/4] Make net watchdog timers 1 sec jiffy aligned
On Wed, 30 May 2007 12:55:51 -0700 (PDT)
David Miller <davem@davemloft.net> wrote:

> From: Patrick McHardy <kaber@trash.net>
> Date: Wed, 30 May 2007 20:42:32 +0200
>
> > Stephen Hemminger wrote:
> > >>>Index: linux-2.6.22-rc-mm/net/sched/sch_generic.c
> > >>>===================================================================
> > >>>--- linux-2.6.22-rc-mm.orig/net/sched/sch_generic.c 2007-05-24 11:16:03.000000000 -0700
> > >>>+++ linux-2.6.22-rc-mm/net/sched/sch_generic.c 2007-05-25 15:10:02.000000000 -0700
> > >>>@@ -224,7 +224,8 @@
> > >>> if (dev->tx_timeout) {
> > >>> if (dev->watchdog_timeo <= 0)
> > >>> dev->watchdog_timeo = 5*HZ;
> > >>>- if (!mod_timer(&dev->watchdog_timer, jiffies + dev->watchdog_timeo))
> > >>>+ if (!mod_timer(&dev->watchdog_timer,
> > >>>+ round_jiffies(jiffies + dev->watchdog_timeo)))
> > >>> dev_hold(dev);
> > >>> }
> > >>> }
> > >>
> > >>Please cc netdev on net patches.
> > >>
> > >>Again, I worry that if people set the watchdog timeout to, say, 0.1 seconds
> > >>then they will get one second, which is grossly different.
> > >>
> > >>And if they were to set it to 1.5 seconds, they'd get 2.0 which is pretty
> > >>significant, too.
> > >
> > >
> > > Alternatively, we could change to a timer that is pushed forward after each
> > > TX, maybe using hrtimer and hrtimer_forward(). That way the timer would
> > > never run in normal case.
> >
> >
> > It seems wasteful to add per-packet overhead for tx timeouts, which
> > should be an exception. Do drivers really care about the exact
> > timeout value? Compared to a packet transmission time its incredibly
> > long anyways ..
>
> I agree, this change is absolutely rediculious and is just a blind
> cookie-cutter change made without consideration of what the code is
> doing and what it's requirements are.
>

what about the obvious compromise:

--- a/net/sched/sch_generic.c 2007-05-30 11:42:18.000000000 -0700
+++ b/net/sched/sch_generic.c 2007-05-30 13:29:34.000000000 -0700
@@ -203,7 +203,11 @@ static void dev_watchdog(unsigned long a
dev->name);
dev->tx_timeout(dev);
}
- if (!mod_timer(&dev->watchdog_timer, round_jiffies(jiffies + dev->watchdog_timeo)))
+
+ if (!mod_timer(&dev->watchdog_timer,
+ dev->watchdog_timeo > 2 * HZ
+ ? round_jiffies(jiffies + dev->watchdog_timeo)
+ : jiffies + dev->watchdog_timeo))
dev_hold(dev);
}
}



--
Stephen Hemminger <shemminger@linux-foundation.org>
-
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