netdev - Re: [PATCH 3/4] Make net watchdog timers 1 sec jiffy aligned

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Message-ID: <465DC598.5060407@trash.net>
Date:	Wed, 30 May 2007 20:42:32 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Stephen Hemminger <shemminger@...ux-foundation.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Venki Pallipadi <venkatesh.pallipadi@...el.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	netdev@...r.kernel.org
Subject: Re: [PATCH 3/4] Make net watchdog timers 1 sec jiffy aligned

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 ..

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