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Name: Stephan Keil
eMail: Stephan.Keil@gmx.de
Date: June 10, 2003 at 10:25:22
Subject: Re: Hyperthreading and 'lock' prefix
In Reply To: Re: Hyperthreading and 'lock' prefix by
unknown on June 10, 2003 at 09:56:17
Text: || Both processors share the same pipeline. If the pipeline would care
|| about read-modify-write conflicts regardless of the executing
|| thread (as it does for a single thread), then it would be safe to omit
|| the 'lock'. So my question refers more to the current implementations
|| of hyperthreaded processors (P4-XEON?!): does the P4 pipeline care about
|| those conflicts regardless of the executing thread?
|
| You are sure it doesn't pick and choses from a random stream of microcode instructions to fill all available execution units? I suspect the dispatcher doesn't much care which thread it comes from, at that level it's probably transparent.
|

I am not sure, but for a single processor (at least for the x86-familiy),
each instruction is executed as if it the instruction stream were
sequential and each instruction were atomic, although the instructions
might be executed out of order and each instruction might be executed
in multiple steps. If the dispatcher doesn't care about threads but sees
a single instruction stream: fine, then it guarantees that each instruction
is executed atomically :)


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