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

On Wed, May 30, 2007 at 12:55:51PM -0700, David Miller wrote:

From: Patrick McHardy <redacted>
Date: Wed, 30 May 2007 20:42:32 +0200

quoted

Stephen Hemminger wrote:

quoted

quoted

quoted

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 are you agreeing with, Dave?

Are you agreeing that "it seems wasteful to add per-packet overhead"?
This patch is not doing that.

A quick grep shows that most things are using multi-second timeouts
here. Of the ones that aren't, a number are using .4s, and many more
aren't even in units of HZ. Makes me wonder if the various boards
using 50ms are being overzealous.

-- 
Mathematics is the supreme nostalgia of our time.