Re: [GIT PULL] sched/core for v2.6.32

On Sun, 13 Sep 2009, Mike Galbraith wrote:

On Sun, 2009-09-13 at 00:07 +0200, Jesper Juhl wrote:
On Sat, 12 Sep 2009, Ingo Molnar wrote:


It was a statistical property based on performance considerations -
and now we flipped it around based on latency and for kbuild
performance/throughput reasons: Serge Belyshev reported a 7%
increase on a quad due to this change and i measured a 1.5%
peak-kbuild performance increase.

Impressive. I wouldn't have expected that much gain by running the parent
first. Actually I personally would have expected child-first to perform
better since (in my experience) it's usually the child that's just forked
that matters the most.

How can waiting for child1 to run a bit before forking off child2 _not_
hurt? The parent is the worker bee creator, the queen bee if you will.
Seems to me that making the queen wait until one egg hatches and ages a
bit before laying another egg is a very bad plan if the goal is to have
a hive full of short lived worker bees.

When I wrote the above, I was thinking of one specific case; a server that
receives a request, forks off a child to handle the request and the
performance we measure is of how long it takes to handle that single
request - and in that specific scenario we want the child to run as soon
as possible.

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Jesper Juhl <jj@xxxxxxxxxxxxx> http://www.chaosbits.net/
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