"One big disparity between the three machines was the Zen 4 machine was outfitted with 512GB of memory, while its competition had just 128GB each"
This feels like cheating to me.
This feels like cheating to me.
No, the actual amount of RAM isn't directly relevant, but it seems like a possible brown m&m to me.
That's exactly where the differences comes from you want to max out the available memory channels on each device not have the same number. Same for latency etc.
I mean your also not fixing the clock speed to 2GHz no boost or when comparing cars limit things just to the first 3 gears or similar.
Because if you would add such artificial limits you won't compare fairly how fast the _max performance_ can be, it would be a very different comparison and wrt. evaluating max performance very unfair.
Now you still need to e.g. have a fair choice of RAM, so preferably if possible use the same RAM sticks (and also use RAM which works equally well with both Intel and AMD). But what that means is that you _have to_ give the AMD system more RAM because it has more channels. Now you also _have to_ make sure that you benchmarks don't have any RAM pressure wrt. capacity.
Also I'm not sure why you mention cache misses? Because number of cache misses is quite independent of RAM amount? Do you mean disk cache or swap misses instead, but I don't think the benchmark does disk I/O and shouldn't have swap either? But even if the benchmark only uses let's say 32GiB of memory for getting a proper GPU
No. Adding that memory bottleneck would make it an unfair and worthless comparison. If you are testing the maximum CPU performance then you need to eliminate those bottlenecks, not create them.
It is not possible to give all the systems the same memory configuration. They don't support the same memory and don't have the same number of channels. And I expect giving all the systems 512 GiB of memory would only widen the lead because larger DIMMs are usually slower.
>Do they expect all of their readers to then audit the code of the benchmarking that they are doing to ensure that it cannot possibly be bound by this?
Cinebench is hardly obscure. The average ExtremeTech reader will already know what it is and what it measures.
you want to max out memory channels on all devices to test max performance
but you also want to use RAM DIMs which are equally good, if possible the same
as AMD has more memory channels this means it will get more "equally good"(1) RAM DIMs and in turn have more memory
and as long as you make sure that no of your benchmarks perform pressure wrt. RAM capacity (e.g. max RAM usage 64GiB) you now have a fair benchmark wrt. max performance
naturally if you don't plan to max out your RAM channels on AMD you do need a different benchmark for non-max performance
(1): "equally good" is also a bit tricky as different vendors have slightly subtle differences in access patterns and DDR5 ram training also can make the same RAM run with different settings on different systems which can make the same ram dim not equally good, but there probably is some RAM which doesn't have such issues
I've read it has 12 channels of DDR5.
With smaller sticks, they could populate all the channels while keeping total memory capacity the same as other setups. I don't see why they had to splurge all the way up to 512GB.
Quoting the article:
"To celebrate the much-hyped launch, our sister site PCMag put the flagship CPU through its paces (remotely) in several popular benchmarks."
The people who did the benchmarks didn't splurge... they had no physical access to the remote machine at all. Certainly, it would have been ideal to talk to their remote contact and see if there were any 16GB sticks sitting around to test with instead, but I agree with the other comments that the memory capacity is unlikely to make a significant difference in these benchmarks.
There will certainly be plenty of other benchmarks soon enough, once people get hands on with these processors.
But the memory is required there to populate the memory channel which push the CPU performance to max.