Re: [PATCH 3/6] cpuset write throttle

[Paul Jackson <pj@sgi.com>]

Peter wrote:
> Perhaps you can keep a proportion in the cpu-set, and do a similar trick
> that the process proportions do.

Beware -- the following comment is made by someone who has been
basically zero attention to this thread, so could be --way-- off
the mark.

Be that as it may, avoid putting anything in the cpuset that you need
to get to frequently.  Access to all cpusets in the system is guarded
by a single global mutex.  The current performance assumption is that
about the only things that need to access the contents of a cpuset are:
 1) explicit user file operations on the special files in the cpuset
    file system, and
 2) some exceptional situations from slow code paths, such as memory
    shortage or cpu hotplug events.

Well ... almost.  If you don't mind the occassional access to the wrong
cpuset, then just taking the task_lock on the current task will guarantee
you that the cpuset pointer in the task struct points to --some-- cpuset,
usually the right one.  This can be (and is) used for some statistic
gathering purposes (look for 'fmeter' in kernel/cpuset.c), where exact
counts are not required.  Perhaps that applies here as well.

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@sgi.com> 1.925.600.0401

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