Re: Linux compatible setaffinity.

Jeff Roberson wrote:
I have implemented a linux compatible sched_setaffinity() call which is somewhat crippled. This allows a userspace process to supply a bitmask of processors which it will run on. I have copied the linux interface such that it should be api compatible because I believe it is a sensible interface and they beat us to it by 3 years.

My implementation is crippled in that it supports binding by curthread only and to a single cpu only. Neither of the schedulers presently support binding to multiple cpus or binding a non-curthread thread. This property is not inherited by forked threads and does not effect other threads in the same process. These two limitations can gradually be weakened without effecting the syscall api.

The linux api is:
int sched_setaffinity(pid_t pid, unsigned int cpusetsize, cpu_set_t *mask);

The cpu_set_t is the same as a fdset for select. The cpusetsize argument is used to determine the size of the array in mask.

I'm mostly interested in feedback on how best to reduce the namespace pollution and avoid pulling the sched.h file into the generated syscall files (sysproto.h, etc). Anyone who feels this is a terrible interface for such a thing should speak up now.

I also feel that in the medium term we will have to deal with machines with more cores than bits in their native word. Using these CPU_SET, CPU_CLR macros is a fine way to deal with this issue.

I also have a primitive 'taskset', although I don't like the name, it allows you to run arbitrary programs bound to a single cpu.


makes sense to me..
don't forget the man page!


Thanks,
Jeff


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