"Putting a large number of these medium-sized cores on a chip is not optimal." - FUD

This comment came from a blog I'm not sure if it was deliberate FUD or the author was just not aware that in today's world the old rules of thumb are no longer relevant.

Today almost all business applications are either multi-threaded or multi-process [firefox, apache, oracle, mysql, postgress, java, ...] So you are more interested in the performance of many threads than a single thread. The old thinking is cache misses are bad do anything to reduce cache misses build a bigger cache, keep other cores away from this cache because when we have a cache miss the processor will stall and that will reduce performance. The real problem is not cache misses but processor stalls. The T1 has 4 hardware threads per core so when we have a cache miss it can work on another thread, the processor doesn't stall. So does the T1 have more cache misses than other processors – maybe, does it reduce the performance of the T1 – No. More theory here more practice here.



[ T: NiagaraCMT CoolThreads CPU ]

Comments:

I made the original comment that you are calling FUD, but I'd like to clarify that we're both right. I would call an Intel Yonah core medium-sized and an UltraSPARC T1 core small, so I stick by my original assertion that putting, say, eight Yonah cores on a chip would be too expensive and hot. Putting eight small cores on a chip appears to work quite well.

Posted by Wes Felter (IBM Research) on February 14, 2006 at 06:23 AM PST #

I understand the point that you were making now, and agree but statements like "medium-sized cores", and "not optimal" are always going mean different things to different people.

Posted by Robin on February 16, 2006 at 09:53 AM PST #

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