Messages in this thread | | | Date | Tue, 2 Sep 2003 22:08:59 -0700 | From | Larry McVoy <> | Subject | Re: Scaling noise |
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On Wed, Sep 03, 2003 at 02:33:56PM +1000, CaT wrote: > I think Anton is referring to the fact that on a 4-way cpu machine with > HT enabled you basically have an 8-way smp box (with special conditions) > and so if 4-way machines are becoming more popular, making sure that 8-way > smp works well is a good idea.
Maybe this is a better way to get my point across. Think about more CPUs on the same memory subsystem. I've been trying to make this scaling point ever since I discovered how much cache misses hurt. That was about 1995 or so. At that point, memory latency was about 200 ns and processor speeds were at about 200Mhz or 5 ns. Today, memory latency is about 130 ns and processor speeds are about .3 ns. Processor speeds are 15 times faster and memory is less than 2 times faster. SMP makes that ratio worse.
It's called asymptotic behavior. After a while you can look at the graph and see that more CPUs on the same memory doesn't make sense. It hasn't made sense for a decade, what makes anyone think that is changing? -- --- Larry McVoy lm at bitmover.com http://www.bitmover.com/lm - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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