From owner-freebsd-arch  Sat Jan 25 19: 6:52 2003
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Date: Sat, 25 Jan 2003 22:06:48 -0500 (EST)
From: Jeff Roberson <jroberson@chesapeake.net>
To: Matthew Dillon <dillon@apollo.backplane.com>
Cc: Steve Kargl <sgk@troutmask.apl.washington.edu>,
	Robert Watson <rwatson@FreeBSD.ORG>,
	Gary Jennejohn <garyj@jennejohn.org>, <arch@FreeBSD.ORG>
Subject: Re: New scheduler (#2)
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On Sat, 25 Jan 2003, Matthew Dillon wrote:

>     I found another problem.  In sched_exit() you are 'returning'
>     part of the child's priority and interactivity to the parent, but
>     you are not taking into account batch processes.
>
>     A batch child which is exiting, such as the 'cc1' in a 'cc' or the 'cc'
>     in a 'make' (you see where this is leading?  Consider a 'make buildworld')
>     must penalize the parent so the next fork/exec'd child retains the batch
>     priority.
>
>     The 4bsd code does this.  The sched_smp code does not.  The sched_smp
>     code simply adds to kg_slptime and this can *never* penalize the parent.
>     The result is that the parent retains its near-zero cpu utilization
>     (because all it is doing is fork/exec/wait).
>
>     This could be the primary cause of the interactive/buildworld latency
>     reports.
>

Ah, yeah, very good.  I hadn't considered the fork/exit priority
adjustments in this light.  I did have a big XXX there to look at this
later though.  I'll see if I cant do something more similar to the 4bsd
code here.

Thanks,
Jeff


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