Date: 15 Jan 2002 09:12:35 -0000 From: Mats Lofkvist <mal@algonet.se> To: tlambert2@mindspring.com Cc: imp@village.org, bmilekic@technokratis.com, arch@FreeBSD.ORG Subject: Re: 64 bit counters again Message-ID: <20020115091235.23322.qmail@kairos.algonet.se> In-Reply-To: <3C439B25.27DCCB2D@mindspring.com> (message from Terry Lambert on Mon, 14 Jan 2002 18:59:49 -0800) References: <20020114105859.A24635@technokratis.com> <3C4305E5.65BB32A6@FreeBSD.org> <20020114114911.A24990@technokratis.com> <20020114.130705.84407599.imp@village.org> <3C439B25.27DCCB2D@mindspring.com>
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From: Terry Lambert <tlambert2@mindspring.com>
> > A 64-bit qauntity would take 738734374912 seconds to overflow if the
> > 32-bit one overflowed in 172 seconds. That strikes me as a reasonable
> > enough period of time. If I did the math right, that's on the order
> > of 23 millinia (23425 years).
>
> Actually, it's closer to 4000 years, if the counter is for a
> Gigabit Ethernet running a theoretical max wire speed, where a
> 32 bit byte counter overflows in 32 seconds (1Gbit/S divided by 8
> to get bytes/S).
>
> Enough interfaces to saturate PCI-X drops this to 500 years (8Gbit/S).
>
> The Apple 802.11e FireWire wireless is already at 5Gbit.
>
> The idea that some counter size will never be exceeded by
> technology by the time it is obsolete is what has people
> complaining about 32 bit counters in this thread already;
> are you prepared to make the same base assumption in the
> choice of 64 bit counters? A terabit network could push
> a 64 bit counter over in under 6 months.
And it (a terabit network) would overflow the 1kB modular
counter solution in 35 seconds or so. Yes, I know, larger
blocks than 1kB should be used in the global counter, and
I guess multiple levels of (32-bit) modular counters can
be used to achieve higher limits, but will it still be
cheaper than just using a 64 bit counter?
_
Mats Lofkvist
mal@algonet.se
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