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Date:      Thu, 26 Jan 2006 11:05:32 -0600 (CST)
From:      Randy Schultz <schultz@sgi.com>
To:        freebsd-questions@freebsd.org
Subject:   did something change in SMP scheduling from 5.4 to 6.0?
Message-ID:  <Pine.BSF.4.63.0601261042150.41670@tdream.americas.sgi.com>
In-Reply-To: <006001c61d47$973bccc0$1225a8c0@kittycat>
References:  <006001c61d47$973bccc0$1225a8c0@kittycat>

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Hey all,

I am curious if something changed in the way extra cpus are utilized in 6.0
vs. 5.4 in a SMP kernel.

My system is a dual-proc Xeon box.  When I was using 5.4 top would show
both procs being used roughly the same, e.g. the "C" column usually had
almost as many processes running on the second cpu as on the first.  On
Jan 23 I did a cvsup and compiled a new 6.0-STABLE SMP kernel.  Now 
watching top I rarely see the second proc being used, even though 
roundrobin is enabled.  FWIW, here's some possibly relevant config bits:
Dude ? sysctl -a|egrep smp
kern.timecounter.smp_tsc: 0
kern.smp.forward_roundrobin_enabled: 1
kern.smp.forward_signal_enabled: 1
kern.smp.cpus: 4
kern.smp.disabled: 0
kern.smp.active: 1
kern.smp.maxcpus: 16
Dude ? 
Dude ? sysctl -a|egrep hyperth
machdep.hyperthreading_allowed: 0

I've attached the output of a typical top with some builds running.  
Unfortunately I don't have any saved data from 5.4.

I do see the second processor being used but those times are rare.  When it 
does happen it seems almost exclusively when I'm seriously hammering the 
system.  This makes me think something has changed with 6.0 behind-the-scenes
such that if the system doesn't need the extra power then it sticks to cpu 0.  
I poked around the release notes and handbook but failed to find anything
on this topic.  Am I all wet and simply have something misconfigured or 
indeed all is well with 6.x doing it's thing hugging cpu 0?

--
 Randy    (schultz@sgi.com)  715-726-2832     email bodhisattva     <*>

 "There is no fire like passion, there is no shark like hatred,
 there is no snare like folly, there is no torrent like greed."

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