Add support for Performance / Efficency cores.

[FractalFir]

(Hopefully) fixes: #2008 on Linux.

Uses directories /sys/devices/ to detect if the system has a "Performace-Hybrid" architecture(has P and E cores). If P cores are detected, forces the benchmark to only run on Performance cores using taskset.

Changes the P-core specific perf events cpu_core/instructions:u/ to "normal" events instructions:u. I am a bit unsure if my implementation of that is correct, tough.

[FractalFir]

It seems like this repo is using a fairly old version of Rust( 1.75.0 which is 1 year old) in its CI.

Is there a reason this can't be raised(eg. MSRV)? If so, I can adapt this patch to use older Rust.

[Kobzol]

It seems like this repo is using a fairly old version of Rust( 1.75.0 which is 1 year old) in its CI.

I like that Rust is bringing an "always up-to-date" philosophy, so that a year old version is considered to be "fairly old" 😆

I don't think that it's needed to stay on 1.75, feel free to update to a newer version, I'd say 1.82 the newest.

[Kobzol]

I don't have P/E cores, so I can't test this, but I assume that it works for you. @bjorn3 Since you created #2008, could you please test if this patch helps to make rustc-perf work on your P/E system?

[FractalFir]

I don't have P/E cores, so I can't test this, but I assume that it works for you.

I think it works for me(I can see the profiling results), but I also don't know enough about rustc-perf to conform that the numbers are accurate.

[Kobzol]

Could you send some icount results for a few benchmarks? Just so that we can compare. And also the number of (P) cores that you have.

[lqd]

Could you also rustfmt your code please, as well as fixing the unused warnings? (there seem to be a few typos in there as well). Thanks.

[FractalFir]

It looks like some of the CI failures are caused by code I did not touch. I don' think fixing them in this PR would be right - I can fix them in another PR if needed.

I think I caught all the typos in comments.

As for the icounts, I only have the ones for an experimental patch to rustc. They are different from the ones on the website, but that might just be caused by the patch in question. I guess I'll have to run a benchmark on the baseline compiler.

For summary-check they are(taken from the graph):
1.461 incr-full
1 full
0.887 incr-patched
0.387 incr-unchanged
For bitmaps-3.1.0-opt, they are roughly

10.81 G incr-full
7.64 G full
3.21 G incr-patched
2.66 G incr-unchanged

I have 8 P cores(12 if you count the ones from hyper-threading) .

[Kobzol]

Interesting. I have this:

With the stable compiler (1.84.1), on a PC with 8 cores. The ratios are similar, but the absolute counts are quite different.

[Kobzol]

The CI failures appeared because you bumped the toolchain, so clippy now has new issues with the code :) I'll update it to 1.81 in a separate PR.

[Kobzol]

#2042

[Kobzol]

It would be better to rebase on top of master and then force-push, than to create the merge commit. You can check https://rustc-dev-guide.rust-lang.org/git.html#rebasing for some hints.

[FractalFir]

I fixed the suggestions made here:

1. The entire thing is now properly rebased
2. Added some comments explaining why E cores are not used.
3. Added a warning message, informing the user that only P cores are used.
4. CARGO_BUILD_JOBS is now set to the P core count, to reflect the restriction to only use P cores.

[Kobzol]

Thanks! I appreciate that you took the time to fix this issue.

Since rustfmt choked on your code, I becometh rustfmt in the latest commit.