On 6/20/22 13:17, Zbigniew Jędrzejewski-Szmek wrote:
Actually, in the cases in the past where I looked at Phoronix benchmarks,
Clear got most of it's performance advantage from defaulting to "Performance"
setting of the CPU, while almost everyone else defaults to "Balanced".
I'd be surprised if that were true, because a system in "balanced" mode
should scale its CPU frequency up when the system is busy. For systems
that aren't constantly busy, the "balanced" mode will usually result in
some jitter in response time depending on what state a given core is in
when the request is made, while a "performance" mode system should be
more predictable. But for a heavily loaded system, there shouldn't be
much difference.
But we don't have to speculate about that too much. Phoronix publishes
its benchmark suite as a container image and since we're interested in
how the power management affects performance in this case rather than
how the supporting OS configuration affects the tools, we can use that
container image.
$ podman run --rm -it phoronix/pts
Within the container, I can run "benchmark system/compress-zstd" to run
a processor-focused benchmark where Clear and Fedora differed
significantly under a "balanced" config and a "performance" config and
observe the results. In Phoronix's test, the result for "Zstd
Compression Compression Level: 3, Long Mode - Compression Speed" under
Clear Linux was 1192.4 MB/s, and under Fedora it was 292.7 MB/s. On my
Fedora system, the results are statistically indistinguishable when I
run that benchmark under "balanced" and under "performance." I get
410.5 MB/s under a balanced profile and 410.7 under performance.
That does not prove that the CPU micro-architecture is the most
significant difference between the two, but it does strongly suggest
that the CPU power settings are not a significant factor in these
differences.
And I'd take the results for RHEL + downstreams with a grain of salt too.
In particular, CentoOS Stream and AlmaLinux get opposite places in various
bechmarks, which doesn't fit well the hypothesis above…
Alma is release 8 and CentOS Stream is release 9. I am not surprised
that there are some benchmarks where they differ. I would, however, be
fairly surprised if benchmarks showed significant differences between
RHEL, Alma, and CentOS Stream 8, or RHEL, Alma, and CentOS Stream 9.
I'd like to see benchmarks before accepting this as a fact.
Aren't we looking at them? :)
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