Opteron vs Athlon

[hurtstotalktoyou]

Since the advent of s939 Opterons, folks have been raving about their 1MB L2 cache. What they don't mention is that their clock speeds are lower. Conventional wisdom seems to dismiss this problem as solved by overclocking, but is it really? Can a 1.8GHz Opteron 165 really match the top overclocking speed of the cheaper Athlon 64 X2 3800+? And can the 2.0GHz Opteron 146 really beat the cheaper 2.2GHz Athlon 64 3500+?

L2 cache certainly has an impact on performance, but a lot of applications don't seem to care if a CPU has 128KB or 1MB L2. If the maximum clock speed of a given CPU is greater than another, how much does the L2 size matter?

 

[jiffylube1024]

Apparently the single core Opterons (or at least early batches of them) were overclocking very well, 2.7+ Ghz.

The Dual core S939 Opterons seem to be doing a more grounded 2.4-2.6 Ghz; more or less in line with the overclocking of a 3800+. The cache difference is minimal.

Btw, many programs (especially games) do care very much if a CPU has 128K or 1MB of L2. Level 2 cache has diminishing returns, but there are very large and tangible gains from 0 > 128K > 256K and a big jump from 256K > 512K of L2. L2 cache size is the reason there is such a big performance gap between Celerons/Semprons and Pentiums/Athlons. But after 512K it really does start to taper off, with the jump from 512K > 1MB being less than a 200MHz clockspeed improvement (on AMD) and the 1MB to 2MB jump on P4 having less of an effect still.

 

[hurtstotalktoyou]

Well, I'm not saying that L2 doesn't matter, only that clock speed usually seems to trump it.

2.4-2.6 GHz is a pretty wide margin. Can we narrow this down a bit? How far can the 165 go on retail cooling? How far can the 3800+ go?

 

[saechaka]

well i got my opteron 144 yesterday. i was so excited i forgot to write down the stepping. i'm at 2.7ghz w/4%overvolt = 1.4v htt=300ht. this is w/stock cooler on dfi board. i had a venice that could hit about 2.5ghz before. i'm pretty glad i made the switch.

 

[Leper Messiah]

Originally posted by: hurtstotalktoyou
Well, I'm not saying that L2 doesn't matter, only that clock speed usually seems to trump it.

2.4-2.6 GHz is a pretty wide margin. Can we narrow this down a bit? How far can the 165 go on retail cooling? How far can the 3800+ go?

You can't really narrow it down any more and be even somewhat accurate. Depending on the the week, stepping, hell, even the different batches of silicon, you can vary quite a bit in maximum attainable clock speed.

Plus, no other varibles are mentioned. What would be the maximum vcore one would consider to be safe? Motherboard, PSU, etc. all play a role in maximum OC. The retail cooling for a 165 IIRC is the same heat pipe design used on the 4200+ and higher X2s, but the 3800+ has the same HSFU that came on my winchester 3000+.

 

[Elfear]

Originally posted by: hurtstotalktoyou
Since the advent of s939 Opterons, folks have been raving about their 1MB L2 cache. What they don't mention is that their clock speeds are lower. Conventional wisdom seems to dismiss this problem as solved by overclocking, but is it really? Can a 1.8GHz Opteron 165 really match the top overclocking speed of the cheaper Athlon 64 X2 3800+? And can the 2.0GHz Opteron 146 really beat the cheaper 2.2GHz Athlon 64 3500+?

L2 cache certainly has an impact on performance, but a lot of applications don't seem to care if a CPU has 128KB or 1MB L2. If the maximum clock speed of a given CPU is greater than another, how much does the L2 size matter?

Seems like the 146's are overclocking a LOT better than their desktop counterparts. My 3700+ San Diego maxed out at 2.85GHz at 1.65V and that was just game stable, Prime would only run for about 18 minutes. My little 146 Opteron can Prime away all day at 2.8GHz@1.39V and is game stable at 3.05GHz@1.49V.

 

[hurtstotalktoyou]

Wow, that's pretty impressive. Thanks for the info!

What about the 165, though, compared to the X2 3800+?

 

[dexvx]

The die probably came from the same wafer, just that Opterons go through more validation than Athlons to make it server grade.