Gipsel (abc@def.com) on 5/22/07 wrote:
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>Intel changed more or less their definition of a µOp with the introduction of the
>PentiumM (later renamed to core, the ones which incorporate µOp fusion). They don't
>differentiate between fused µOps and not fused ones. When looking at the possible
>µOps fused together you really get the impression that intel more or less adopted
>AMDs concept of MacroOps consisting of an ALU µOp and and load-store µOp. Both (fused
>µOps and MacroOps) get split up in two individual µOps later in the pipeline. Agner
>is absolutely right that they are more or less equivalent.

I just wonder how often such a fusion is happening, while it seems a macro-op is holding two micro-ops (an integer/fp operation, and a load/store/load-store one) most of the time.

>But I don't think Core2 is really that much wider than Barcelona. First you have
>to consider that Core 2 has more restrictions to its 4 decoders (only one complex
>one, smaller fetch bandwidth and smaller predecode buffer). It's clear that core2
>is not able to sustain a higher decode rate than Barcelona on all workloads.

I did exactly this in some of my earlier posts in this thread.

> Additionally
>the core2 has a six issue execution core, but only three issue ports can accept
>arithmetical instruction. The other three issue ports only accepts memory operations.
>That means the peak execution rate is also not necessarily higher on core2 than
>on K8/Barcelona. But the 4µOp execution rate of the Core2 will help if you have
>some "RISCy" x86 code, that means separate load instruction followed by register
>operations instead of load-use operations (but core2 should still prefer one load-use operation over two separate ones).
>
>>(BTW, Agner is using micro-op all along, also on Intel's CPUs, instead of uop. uop
>>is perhaps just a witty abbrevation, isn't it?)
>
>Exactly. Actually it isn't uOp, it's µOp. As you know, "µ" is the greek letter
>"micro". Most keyboards simply lack a key for that letter.

Of course, but there is no µ on my keyboard. :) It's common to use a u instead of µ.