netdev - Re: [PATCH] Rate should be u64 to avoid integer overflow at high speeds (>= ~35Gbit)

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Message-ID: <513F3BE1.2080409@genband.com>
Date:	Tue, 12 Mar 2013 08:29:53 -0600
From:	Chris Friesen <chris.friesen@...band.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Bill Fink <billfink@...dspring.com>, Vimal <j.vimal@...il.com>,
	netdev@...r.kernel.org, shemminger <shemminger@...tta.com>
Subject: Re: [PATCH] Rate should be u64 to avoid integer overflow at high
 speeds (>= ~35Gbit)

On 03/09/2013 11:54 PM, Eric Dumazet wrote:
> On Sun, 2013-03-10 at 00:49 -0500, Bill Fink wrote:
>
>> I don't see the problem.  An old program would not know about
>> the new multiplier, would thus get the default multiplier of 1,
>> and get the same behavior as always, with the same limitation
>> of ~34 Gbps.  But someone with a newer tc/kernel could for example
>> specify a multiplier of 10, which would then support rates up to
>> about 340 Gbps.  It sounds like a reasonable approach to me.
>
> Hopefully, some of us see the problem here and are able to reject
> patches before breaking user land.

The only problem I see is that you can't set the multiplier with a new 
tool and then query the rate with old tools.

But you're going to run into that problem with the old tools no matter 
what you do--and not doing anything is a crappy option as well.

Some kind of multiplier or shift makes as much sense as anything else. 
With old tools you get current behaviour, with new tools you can specify 
a multiplying factor to trade off resolution vs precision.

Chris
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