Re: (1/4) [PATCH] cpuset -- 2.6.0-test8

[William Lee Irwin III]

On Tue, 21 Oct 2003, William Lee Irwin III wrote:
>> Best not to insist NR_CPUS % BITS_PER_LONG == 0.

On Wed, Oct 22, 2003 at 04:34:21PM +0200, Simon Derr wrote:
> Actually we don't, but you're right, NR_CPUS should definately be used
> here.

The insistence mentioned was implicit, of course.


On Tue, 21 Oct 2003, William Lee Irwin III wrote:
>> Unfair rwlocks can take boxen out when abused by quadratic algorithms.

On Wed, Oct 22, 2003 at 04:34:21PM +0200, Simon Derr wrote:
> I don't see exactly which lock you are talking about here ?
> Anyway, the current state of the cpusets is OK for a 'gentle' use. I'm
> sure some improvements are needed to protect it from 'evil' users ;-)

tasklist_lock, infamous for setting off the NMI oopser (i.e. watchdogs
that panic machines when interrupts are ignored for long periods of
time) when users run many instances of top(1) or other nonsense. Not
a performance concern per se, but it may very well be hopeless anyway.

There are several threads about the rwlock algorithms being unfair and
taking out machines and/or persistently starving writers. Probably the
most recent one was started by Kevin van Maren. There Linus suggested
eventually adding a fair rwlock primitive to address this.


-- wli
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