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Date:      Sun, 1 Jul 2001 20:13:27 -0500
From:      Greg Lehey <grog@FreeBSD.org>
To:        "Andrew C . Hornback" <hornback@wireco.net>, Alexandr Alov <amil_98@chat.ru>, Linh Pham <lplist@closedsrc.org>
Cc:        freebsd-questions@FreeBSD.org
Subject:   Number of processors for SMP (was: Question of day.)
Message-ID:  <20010701201327.B418@sydney.worldwide.lemis.com>
In-Reply-To: <004801c101d3$ba4cb100$0e00000a@tomcat>; from hornback@wireco.net on Sat, Jun 30, 2001 at 10:15:41PM -0400
References:  <01063023314202.14971@max.myhome.ru> <Pine.BSF.4.33.0106301222370.37626-100000@q.closedsrc.org> <01063023314202.14971@max.myhome.ru> <Pine.BSF.4.33.0106301152310.37556-100000@q.closedsrc.org> <004801c101d3$ba4cb100$0e00000a@tomcat>

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On Saturday, 30 June 2001 at 22:15:41 -0400, Andrew C. Hornback wrote:

> On  Saturday, June 30, 2001 2:54 PM, Linh Pham wrote:
>> To: Alexandr Alov
>> Cc: freebsd-questions@FreeBSD.org
>> Subject: Re: Question of day.
>>
>>
>> On 2001-06-30, Alexandr Alov scribbled:
>>
>> # What maximum quantity of processors can support FreeBSD 4.3 ?
>>
>> I've seen FreeBSD 4.x installations with four Intel Xeon processors...
>> but with the current SMP code, you probably won't be able to take
>> complete advantage of all four processors. SMPng in FreeBSD 5.x is
>> supposed to take SMP performance to a much higher notch.
>>
>> Haven't been able to get my hands on a eight-way server yet :)
>
> 	I've seen FreeBSD 4.2-Release running on a 6 way machine, and this was
> about 5 months ago.  Worked like a charm, and a good thing too, since I'm
> building one of these "monsters" myself...
>
> 	Given the technology that's out there, the most IA processors
> I've ever heard of in a machine would be the new Unisys CMP-7000
> (Model number might be wrong) with up to either 32 or 64 processors
> per box... needless to say, it'll be a while before I get one of
> those as a workstation.  *evil grin*

I don't think there's any particular hard limit in the number of
processors.  In general, the incremental benefit of adding more
processors will diminish as you increase the number.  I'd guess that 8
processors will work, but that the 32/64 processor machines will not
work for reasons not directly related to the number of processors.


On Saturday, 30 June 2001 at 23:21:33 +0400, Alexandr Alov wrote:
>> I've seen FreeBSD 4.x installations with four Intel Xeon processors...
>> but with the current SMP code, you probably won't be able to take
>> complete advantage of all four processors. SMPng in FreeBSD 5.x is
>> supposed to take SMP performance to a much higher notch.
>>
>> Haven't been able to get my hands on a eight-way server yet :)
>
> Thank for the answer.
> Only four?
> In general that is necessary eight.
> How with such quantity ?

It depends on what you want to do with them.  The real issue is
contention for the kernel.  If you are doing compute-bound work, the
additional CPUs will be very useful.  If you're I/O bound, you'll
quickly reach the point of diminishing returns.

On Saturday, 30 June 2001 at 12:25:31 -0700, Linh Pham wrote:
> On 2001-06-30, Alexandr Alov scribbled:
>
> # Thank for the answer.
> # Only four?
>
> You can probably get FreeBSD to install on 8+ processor servers, but
> with my experience... I have only worked with machines with four
> processors.
>
> # In general that is necessary eight.
>
> Remember, the standard version of Windows 2000 only handles up to four
> processors ;-)

Well, I didn't know that, but I can't see that it's very relevant.



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