Re: 2.5 Changes doc update.

From: Robert Love (
Date: Wed Dec 11 2002 - 14:46:51 EST

On Wed, 2002-12-11 at 12:25, Dave Jones wrote:

> Process scheduler improvements.
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> - Another much talked about feature. Ingo Molnar reworked the process
> scheduler to use an O(1) algorithm. In operation, you should notice
> no changes with low loads, and increased scalability with large numbers
> of processes, especially on large SMP systems.
> - Robert Love wrote various utilities for changing behaviour of the
> scheduler (binding processes to CPUs etc). You can find these tools at
> - Regressions to and

Two notes here:

- The behavior of sched_yield() changed a lot. A task that uses
  this system call should now expect to sleep for possibly a very
  long time. Tasks that do not really desire to give up the
  processor for a while should probably not make heavy use of this
  function. Unfortunately, some GUI programs (like Open Office)
  do make excessive use of this call and under load their
  performance is poor. It seems this new 2.5 behavior is optimal
  but some user-space applications may need fixing.

- The above applies to use of yield() in the kernel, too.

- 2.5 adds system calls for manipulating a task's processor
  affinity: sched_getaffinity() and sched_setaffinity()

        Robert Love

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