automatic parallelizing of 2 threads in a dual core ??

If I write a multithread program with pthreads on a Linux platform, do I have to expect threads run parallel on the two cores automatically (of course as long as there are not threads waiting for others or for events like I/O) or is there some probability that they run on one core only unless I use some directive or whatever??

Thank you

They will run on both threads unless there are other threads that want to run at the same time. Which thread ends up on which core and how long they stay that way is entirely random.

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Mats

Quote:

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Originally Posted by matsp

They will run on both threads unless there are other threads that want to run at the same time. Which thread ends up on which core and how long they stay that way is entirely random.

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Mats

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ok so if in the system i know that most CPU is used by my program and I manage to split the most of the job in at least 2 threads I can expect time elapsed to decrease close to 1/2 ?
(considering no false sharing and so on)

Yes, if your two threads are mostly CPU bound, and not dependant on each other, then half the time or close to that is what you can expect.

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Mats

thank you very much!!