Andrei F (andrei.delete@this.anandtech.com) on November 18, 2020 8:34 am wrote:
> Dummond D. Slow (mental.delete@this.protozoa.us) on November 18, 2020 7:48 am wrote:
> > Andrei F (andrei.delete@this.anandtech.com) on November 18, 2020 7:44 am wrote:
> > > Chester (lamchester.delete@this.gmail.com) on November 18, 2020 7:02 am wrote:
> > >
> > > > Sure, Cinebench isn't the best representation of average workloads. But SPEC is far
> > > > worse. No consumer cares about SPEC. The subtests are mostly based off applications
> > > > no one uses, or very specific scientific simulations. It's even useless as a benchmark
> > > > to see whether your system is working properly, because it's so overpriced.
> > > >
> > > > Even when they base a subtest off something a consumer might
> > > > do, the results are hilariously off. For example:
> > > > Encoding a 4K video using ffmpeg libx264 slow preset, on Haswell locked to 2.2 GHz
> > > > - affinity set to 4 threads: 6.6 fps
> > > > - no affinity set: 7.6 fps (1.15x scaling)
> > > >
> > > > 525.x264_r test: 1.0315x scaling
> > > >
> > > > A quick look at the benchmark description shows them using -bitrate 1000.
> > > > If that's 1 kbps (or 1 mbps) bitrate, it's hilariously unrealistic.
> > > >
> > > > Now take AT Bench's POV-Ray scores for the i5-6600K (1741, 3.6 GHz all core turbo)
> > > > and i7-6700K (2419, 4.2 GHz all core turbo). Scaling down the 6700K's score to account
> > > > for clock speed difference gives 2073. SMT scaling would be roughly 1.19x
> > > >
> > > > 511.povray_r: 1.0291x scaling.
> > > >
> > > > What's going on?
> > > >
> > > > Also, some SPEC numbers make it seem like negative SMT scaling is common. It's not. I've
> > > > personally never seen an application that can use all available threads do worse when
> > > > SMT is enabled. Can we stop looking at the irrelevant pile of garbage that is SPEC?
> > > >
> > > > And what makes you claim "Cinebench has long dependency chains"? How do you
> > > > know SMT scaling is from that rather than hiding cache misses better?
> > >
> > > Because Maxon developers *literally told us that*. There's apparently
> > > a lot of random accesses to the BVH of the scene.
> > >
> > > The CB23 score on the M1 goes from 5601 to to 7819 when comparing just the big cores to having
> > > both the big and small cores together. Explain to me how that happens that the SoC gets 39% more
> > > throughput from cores that are 1/4th the performance? It's an extreme showcase of a dependency
> > > workload that scales extremely well with threads - again, straight from the Maxon devs.
> >
> > Interesting but "long dependency chains"don't disqualify it as a benchmark, does
> > it. I doubt that it is very expceptional and no other software does that.
>
> I'm not saying that it's a bad benchmark or that it should be disqualified,
> it's going to be representative of Cinema4D, but people should understand what
> it does and not use it as the overall representation of MT performance.
>
> >
> > I hope eventually we get some very comparable HT/noHT CPU in AnandTech benchmark for comparing,
> > in the meantime I found this https://www.anandtech.com/bench/product/2622?vs=2652
> > Skylake @ 3,8-4,2GHz 4c/4t versus 4,0-4,2 4c/8t (sadly also has more L2 cache due to Intel's segmenting).
>
> It's something in the pipeline. Generally gaming will benefit turning off SMT even.
>

Yeah, games I agree with, that's where SMT being useless or a minus does happen quite often (it's not a rule though). I kind of only care about applications and didn't realize that changes things quite/should have been stated as a caveat.