Re: [Announce] [patch] Modular Scheduler Core and Completely FairScheduler [CFS]

[Andrew Morton]

On Thu, 19 Apr 2007 05:18:07 +0200 Nick Piggin <npiggin@xxxxxxx> wrote:

> And yes, by fairly, I mean fairly among all threads as a base resource
> class, because that's what Linux has always done

Yes, there are potential compatibility problems.  Example: a machine with
100 busy httpd processes and suddenly a big gzip starts up from console or
cron.

Under current kernels, that gzip will take ages and the httpds will take a
1% slowdown, which may well be exactly the behaviour which is desired.

If we were to schedule by UID then the gzip suddenly gets 50% of the CPU
and those httpd's all take a 50% hit, which could be quite serious.

That's simple to fix via nicing, but people have to know to do that, and
there will be a transition period where some disruption is possible.

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