netdev - Re: txqueuelen has wrong units; should be time

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Date:	Sun, 27 Feb 2011 08:54:12 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Mikael Abrahamsson <swmike@....pp.se>
Cc:	Albert Cahalan <acahalan@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	netdev@...r.kernel.org
Subject: Re: txqueuelen has wrong units; should be time

Le dimanche 27 février 2011 à 08:02 +0100, Mikael Abrahamsson a écrit :
> On Sun, 27 Feb 2011, Albert Cahalan wrote:
> 
> > Nanoseconds seems fine; it's unlikely you'd ever want
> > more than 4.2 seconds (32-bit unsigned) of queue.
> 
> I think this is shortsighted and I'm sure someone will come up with a case 
> where 4.2 seconds isn't enough. Let's not build in those kinds of 
> limitations from start.
> 
> Why not make it 64bit and go to picoseconds from start?
> 
> If you need to make it 32bit unsigned, I'd suggest to start from 
> microseconds instead. It's less likely someone would want less than a 
> microsecond of queue, than someone wanting more than 4.2 seconds of queue.
> 

32 or 64 bits doesnt matter a lot. At Qdisc stage we have up to 40 bytes
available in skb->sb[] for our usage.

Problem is some machines have slow High Resolution timing services.

_If_ we have a time limit, it will probably use the low resolution (aka
jiffies), unless high resolution services are cheap.

I was thinking not having an absolute hard limit, but an EWMA based one.



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