[RFC PATCH v1 00/57] Boot-time page size selection for arm64

[Petr Tesarik]

Hi Ryan,

On Thu, 17 Oct 2024 13:32:43 +0100
Ryan Roberts <ryan.roberts at arm.com> wrote:

>[...]
> I understand that Suse might be able to help with wider performance testing

Sorry for the delay (vacation, other tasks). Anyway, let me share some
results with you.

First, I have looked only at 4k pages (constant v. selected at boot
time) so far.

Second, the impact of the patch series is much smaller than I expected.
Most macro-benchmarks (dbench, io-bench) did not see any significant
slowdown. There appears to be a performance hit of approx. 1-2%, but
that's within noise, and I can't dedicate my time to running extensive
tests to find the distribution peak and compare. In short, I suspect a
slight performance hit, but I cannot quantify it.

Third, a few micro-benchmarks saw a significant regression.

Most notably, getenv and getenvT2 tests from libMicro were 18% and 20%
slower with variable page size. I don't know why, but I'm looking into
it. The system() library call was also about 18% slower, but that might
be related.

The dup() syscall was up to 5% slower (depends on underlying filesystem
type).

VMA unmap was slower for some sizes, but the pattern seemed random,
sometimes giving even better performance with variable page size, so
this micro-benchmark may be too unstable to draw any conclusions.

Stay tuned
Petr T