Messages in this thread | | | Subject | Re: [PATCH] 2.5: task cpu affinity syscalls | From | Robert Love <> | Date | 11 Apr 2002 15:00:03 -0400 |
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On Thu, 2002-04-11 at 10:23, Aneesh Kumar K.V wrote:
> Now that we have API that allow a process to say I would like to go to > these CPU, Are there any API's available that will allow a CPU to say I > will take only these process. ( Resource Affinity domains ? )
First, the Linux scheduler is not really designed to do this. It's cpu affinity works on a per-process basis and in fact needs to explicitly move CPUs from each CPU. Second, we could probably do this in userspace using the exported sched_setaffinity syscall (just loop over all tasks, setting the affinity as-needed).
There is a problem, though. In 2.5 with the O(1) scheduler, if the process is not currently running on an allowed CPU when it is affined, it must be forced off to a legal CPU via the migration threads. This is expensive and complex and _not_ something we want to do to every process on the system.
For this reason, and because I honestly favor the simple interfaces I wrote, I think we should stick with just the exported interfaces we currently have.
This isn't to say we could not do this in userspace - it would not be hard (but still gross to move mass processes around). We could also have a version of init that affines itself on boot, thereby having every other process likewise affined. Then explicitly move away those processes we want elsewhere. This is cheap and easy.
Robert Love
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