From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <49AE073B.3070501@orcasystems.com>
Date: Tue,  3 Mar 2009 20:44:43 -0800
From: James Tomaschke <james@orcasystems.com>
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To: Fans of the OS Plan 9 from Bell Labs <9fans@9fans.net>
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Subject: Re: [9fans] threads vs forks
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erik quanstrom wrote:
>> I think the reason why you didn't see parallelism come out earlier in
>> the PC market was because they needed to create new mechanisms for I/O.
>>   AMD did this with Hypertransport, and I've seen 32-core (8-socket)
>> systems with this.  Now Intel has their own I/O rethink out there.
>
> i think what you're saying is equivalent to saying
> (in terms i understand) that memory bandwidth was
> so bad that a second processor couldn't do much work.
Yes bandwidth and latency.
>
> but i haven't found this to be the case.  even the
> highly constrained pentium 4 gets some milage out of
> hyperthreading for the tests i've run.
>
> the intel 5000-series still use a fsb.  and they seem to
> scale well from 1 to 4 cores.

Many of the circuit simulators I use fall flat on their face after 4
cores, say.  However I blame this on their algorithm not hardware.

I wasn't making an AMD vs Intel comment, just that AMD had created HTX
along with their K8 platform to address scalability concerns with I/O.

> are there benchmarks that show otherwise similar
> hypertransport systems trouncing intel in multithreaded
> performance?  i don't recall seeing anything more than
> a moderate (15-20%) advantage.

I don't have a 16-core Intel system to compare with, but:
http://en.wikipedia.org/wiki/List_of_device_bandwidths#Computer_buses

I think the reason why Intel developed their Common Systems Interconnect
(now called QuickPath Interconnect) was to address it's shortcomings.

Both AMD and Intel are looking at I/O because it is and will be a
limiting factor when scaling to higher core counts.

>
> - erik
>
>