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Postby FAMAS » Sun Apr 02, 2017 3:12 pm

has the technology to emulate multiple physical core as 1 logical core been made? if not, why?
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Re: hypothreading

Postby bruce » Fri May 05, 2017 3:25 pm

No, and it won't be.

A logical core maintains a precise ordering of the operations assigned to it which would be disrupted if multiple physical cores were allowed to operate independently on a single task.

When multiple cores are available and you want them to work on a single process, SOMETING must decide which task to assign to each core. The Operating System contains code to assign operations to individual cores. A program which can make use of multiple cores must choose which operations can be run in parallel and which must be serialized. The GROMACS core contains the logic which decides which operations can be assigned to independent cores and then it must periodically synchronize the overall process, waiting on the operations from other streams by causing some cores to wait until the operations assassinated to them reach a point that other operations can continue.

Suppose you're watching a video on one your "hypothreaded" logical core. If operations are randomly assigned to operate on different cores, the sound and the video might become unsynchronized if there's no code to keep them synchronized. Programming for SMP is not so simple as to allow different parts of a single process can proceed independently.
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