On 09/07/1999 18:53 -0400, John F. Nixon wrote:
>> Robert M. Hyatt writes:
>>
>>
>> You are misreading my claim. I'm not saying threads can issue
>> instructions simultaneously. I'm saying the processor can have a
>> mixture of instructions from different threads in execution at once.
>>
Somehow, I think that the thread-switching (context-switching)
code in the kernel is significantly longer than N instructions
where N is the number of pipeline stages in your favorite
processor, rendering this a pretty solidly impossible situation...
Yes, modern processors can execute multiple instructions at once,
and even out of order, but the number of instructions executed
by the kernel to switch from one thread to another is fairly
significant. Until the "next generation" of CPUs is available
that actually do hardware multi-threading, you cannot have
instructions from separate threads (processes/LWPs/whatevers)
running at once. There may be a little overlap where you have
a couple instructions from userspace and a couple from kernel
space running at once for certain system calls, though...
tw
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