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Date:      Thu, 28 Feb 2002 11:44:37 +1030
From:      Greg Lehey <grog@FreeBSD.org>
To:        Stephen C Frost <stephen.c.frost@intel.com>
Cc:        freebsd-questions@freebsd.org
Subject:   Re: FreeBSD, SMP and Performance Speeds?
Message-ID:  <20020228114437.R90450@wantadilla.lemis.com>
In-Reply-To: <B9ECACBD6885D5119ADC00508B68C1EA0288A6E1@orsmsx107.jf.intel.com>
References:  <B9ECACBD6885D5119ADC00508B68C1EA0288A6E1@orsmsx107.jf.intel.com>

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[removing cross-post to -hackers]

On Wednesday, 27 February 2002 at 16:26:35 -0800, Stephen C Frost wrote:
>
> All -
>
> I have RTFM'd, with little luck.  Can some enlightened soul impart knowledge
> upon me, thus letting me know why any kernels compiled with SMP enabled seem
> to be slowing the whole system down?  Throughput goes down by 40%.  Tasks
> take twice as long to run, etc, etc...
>
> I have multiple boxes (Dells, IBM's, Microns, Gateways...) running FreeBSd
> 4.5, all showing the same phenomenon.  I initially mistook it for a NIC
> driver issue, but it appears to be system-wide.  And is directly linked to
> SMP: two kernels, identical EXCEPT that one has SMP enabled, the other not.
> The enabled kernel that *should* be fully utilizing multi-procs is suddenly
> effectively running at half speed.
>
> Is this a config issue?  Any helpful hints?  Or is it better just to keep
> SMP disabled on a multi-proc box?

It's obviously not a general thing, or we wouldn't release SMP code.
It depends very much on what you do, and you haven't said anything
about that.

It would also be interesting to see if you get the same results
running 5-CURRENT.  While this version isn't suited to production use,
it's based on a very different implementation, and the information
would help us work out what's going on here.

Greg
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