Re: [linuxperf] Possible fix for Mindcraft Apache problem

[Rik van Riel <riel@nl.linux.org>]

On Thu, 6 May 1999, Dan Kegel wrote:

> Looks like 2.2.7 fixes a Mindcraft-like problem 
> running the SPECWeb96 benchmark, reported by Karthik Prabhakar.
> See http://www.kegel.com/mindcraft_redux.html#bugs

Uhm, no. The main bug with the web benchmark remains. The
way Linux and Apache 'cooperate', there's a lot of trouble
with the 'thundering herd' problem.

That is, when a signal comes in, all processes are woken up
and the scheduler has to select one from the dozens of new
runnable processes.

> Also, a fellow at DEC found a problem that causes
> wasted CPU in the scheduler under similar conditions,
> and the first trial patch that might help has been posted 
> to linux-kernel already.

The patch mentioned is a patch to increase the scheduler
efficiency. It is nice and I will probably use it as a
basis for my own scheduler patch, but it's not the real
solution.

The real solution is to go from wake-all semantics to
a wake-one style so we won't have the enormous runqueues
the guy at DEC experienced.

The good news is that it's a simple patch that can
probably be fixed within a few days...


cheers,

Rik -- Open Source: you deserve to be in control of your data.
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