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

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Date:	Tue, 12 Mar 2013 15:42:45 +0000
From:	Thomas Graf <tgraf@...g.ch>
To:	Chris Friesen <chris.friesen@...band.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	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 03/12/13 at 08:29am, Chris Friesen wrote:
> 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.

The introduction of a shift operator or multiplier introduces
inprecision. I'd much rather see new 64bit Netlink attributes
that, if present, replace the old rate values and statistics.

You will need to add a new Netlink attribute anyway and we might
as well transfer the actual rate instead of a multiplier. Just
like we did with IFLA_STATS64.
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