Re: [9fans] threads vs forks

["J.R. Mauro" <jrm8005@gmail.com>]

On Tue, Mar 3, 2009 at 11:44 PM, James Tomaschke <james@orcasystems.com> wrote:
> 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.

And soon hard disk latencies are really going to start hurting (they
already are hurting some, I'm sure), and I'm not convinced of the
viability of SSDs.


There was an interesting article I came across that compared the
latencies of accessing a register, a CPU cache, main memory, and disk,
which put them in human terms. As much as we like to say we understand
the difference between a millisecond and a nanosecond, seeing cache
access expressed in terms of moments and a disk access in terms of
years was rather illuminating, if only to me.

Same article also put a google search at only slightly slower latency
than hard disk access. The internet really is becoming the computer, I
suppose.

>
>>
>> - erik
>>
>>
>
>
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