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Hi, does anyone know if gang scheduling is implemented in Linux? And if so, can you recommend any books/articles/site where I can learn more about it? I am trying to implement it on FreeBSD, so if anyone has any information about that, it would be very helpful
Stefan, I don't mean to be a naysayer, but is gang scheduling even implemented at the kernel level?
It was an interesting question, I'd like to thank you for pointing out the concept of "gang scheduling" in distributed computing to me and the rest of the readers but a short review of some documentation (mostly the Wikipedia page) suggests to me that the local kernel level scheduling is probably SCHED_BATCH and "gang" is something the cluster software is handling.
If I'm wrong, I apologize, but to the best of my knowledge, Linux doesn't give you that option (I only know of 5 sched modes SCHED_RR, SCHED_FIFO, SCHED_BATCH, SCHED_IDLE and SCHED_OTHER *other uses CFS or the Completely Fair Scheduler).
The general definition of gang scheduling is inefficient for a single processor, even in an SMP operation. It requires all processors to delay until they all reach a sync point- causing wasted CPU time waiting for the other processors.
You CAN do it in a SMP mode very easily - but you have to have a counting semaphore that all processes are waiting for, then the locking process can release the lock and all processes resume.
It is also inefficient in SMP as the various threads will have different page fault/IO activity that causes them to get out of sync - which reindroduces wasted CPU time.
In a distributed system/cluster, gang scheduling is handled by the job scheduler - but even then, it isn't rigid. All nodes are given work to do, and the results collected - and more work could be sent out. It works, but is a bit on the inefficient side as it requires a lot of message passing - which allows the nodes to get out of sync again.