The Ampere Altra Max Review: Pushing it to 128 Cores per Socket
by Andrei Frumusanu on October 7, 2021 8:00 AM EST- Posted in
- Servers
- Arm
- Neoverse N1
- Ampere
- Altra Max
SPEC - Multi-Threaded Performance - Aggregate
Switching over to the aggregate geomean scores for the suites, we see a more moderate view of the generational improvements of the Altra Max chip:
In the integer suite, the M128-30 only sees a 6-10% advantage over the Q80-33 depending on the 2- or 1-socket scores. It’s a smidge faster than the EPYC 7763, but there’s more considerations to have than just the total scores.
In the floating-point suite, the system also sees rather lacklustre figures of only 3-4% advantage of the M128-30 over the Q80-33.
The general problem of these scores showcase is a trend of the new Altra Max design, and that is that it’s not as general-purpose as we tend to expect for a CPU. Even though we see regular large workload gains of 30-45%, the way the suite is designed for the “base” scores is that we’re running all workloads with the same number of instances, something which at 128 cores on the Altra Max inevitably leads to performance regressions in anything that is more demanding on memory and caches.
When we first heard of the Altra Max only featuring a 16MB cache, we were quite pessimistic of this aspect of the design, well – that was also true of the 32MB cache of the 80-core Altra, where performance in some workloads just can not scale well beyond a certain core count due to the shared resource contention.
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Jurgen B - Thursday, October 7, 2021 - link
Love your thorough article and testing. This is some serious firing power from the Ampere and makes some great competition for Intel and AMD. I really like the 256T runs on the AMD Dual socket EPYCs (they really are serving me well in floating point research computing), but it seems that future holds some nice innovations in the field!mode_13h - Thursday, October 7, 2021 - link
Lack of cache seems to be a serious liability, though. For many, it'll be a deal breaker.Wilco1 - Friday, October 8, 2021 - link
Yet it still beats AMD's 7763 with its humongous 256MB L3 in all the multithreaded benchmarks. Sure, it would be even faster if it had a 64MB L3 cache, however it doesn't appear to be a serious liability. Doing more with far less silicon at a lower price (and power) is an interesting design point (and apparently one that cloud companies asked for).Jurgen B - Friday, October 8, 2021 - link
Yes, Cache will play a role for many. However, people buying such servers likely have a very specific workload in mind. And thus they now have more choices which of the manufacturer options they prefer, and these choices are really good to see. Compared to 10 years ago, when AMD was much less competitive, it is wonderful to see the innovation.schujj07 - Friday, October 8, 2021 - link
That isn't true at all. The SPEC java benchmarks have the Epyc ahead, SpecINT Base Rate-N Estimated they are almost equal (despite having half the cores), FP Base Rate-N Estimated the Epyc is ahead, compiling the Epyc is ahead. Anything that will tax the memory subsystem by not fitting into the small cache of the Altra and the performance is lower for the Altera. Per core performance isn't even close.mode_13h - Saturday, October 9, 2021 - link
Thanks for correcting the record, @schujj07.The whole concept of adding 60% more cores while halving cache is mighty suspicious. In the most charitable view, this is intended to micro-target specific applications with low memory bandwidth requirements. From a more cynical perspective, it's merely an exercise in specsmanship and maybe trying to gin up a few specific benchmark numbers.
Wilco1 - Saturday, October 9, 2021 - link
If you're that cynical one could equally claim that adding *more* cache is mighty suspicious and gaming benchmark numbers. Obviously nobody would spend a few hundred million on a chip just to game benchmarks. The fact is there is a market for chips with lots of cores. Half the SPEC subtests show huge gains from 60% extra cores despite the lower frequency and halved L3. So clearly there are lots of applications that benefit from more cores and don't need a huge L3.Wilco1 - Saturday, October 9, 2021 - link
The Altra Max wins the more useful critical-jOPS benchmark by over 30%. It also wins the LLVM compile test and SPECINT_rate by a few percent. The 7763 only wins SPECFP by 18% (not Altra's market) and max-jOPS by 13%.So yes my point is spot on, the small cache does not look at all like a serious liability. Per-core performance isn't interesting when comparing a huge SMT core with a tiny non-SMT core - you can simply double the number of cores to make up for SMT and still use half the area...
mode_13h - Saturday, October 9, 2021 - link
> Per-core performance isn't interesting when comparing ...Trying to change the subject? We didn't mention that. We were talking only about cache.
> The Altra Max wins the more useful critical-jOPS benchmark by over 30%.
That's really about QoS, which is a different story. Surely, relevant for some. I wonder if x86 CPUs would do better on that front with SMT disabled.
> the small cache does not look at all like a serious liability.
Of course it's a liability! It's just a very workload-dependent one. You need only note the cases where Max significantly underperforms, relative to its 80-core sibling, to see where the cache reduction is likely an issue.
The reason why there are so many different benchmarks is that you can't just seize on the aggregate numbers to tell the whole story.
mode_13h - Saturday, October 9, 2021 - link
Apologies, I now see where schujj07 mentioned per-core performance. I even searched for "per-core" but not "per core".