Uh oh!
There was an error while loading. Please reload this page.
Rollup of 4 pull requests - #84739
Closed
Dylan-DPC-zz wants to merge 9 commits into
Closed
Conversation
On arm64 we have seen on several databases that ISB (instruction synchronization barrier) is better to use than yield in a spin loop. The yield instruction is a nop. The isb instruction puts the processor to sleep for some short time. isb is a good equivalent to the pause instruction on x86. Below is an experiment that shows the effects of yield and isb on Arm64 and the time of a pause instruction on x86 Intel processors. The micro-benchmarks use https://github.com/google/benchmark.git $ cat a.cc static void BM_scalar_increment(benchmark::State& state) { int i = 0; for (auto _ : state) benchmark::DoNotOptimize(i++); } BENCHMARK(BM_scalar_increment); static void BM_yield(benchmark::State& state) { for (auto _ : state) asm volatile("yield"::); } BENCHMARK(BM_yield); static void BM_isb(benchmark::State& state) { for (auto _ : state) asm volatile("isb"::); } BENCHMARK(BM_isb); BENCHMARK_MAIN(); $ g++ -o run a.cc -O2 -lbenchmark -lpthread $ ./run -------------------------------------------------------------- Benchmark Time CPU Iterations -------------------------------------------------------------- AWS Graviton2 (Neoverse-N1) processor: BM_scalar_increment 0.485 ns 0.485 ns 1000000000 BM_yield 0.400 ns 0.400 ns 1000000000 BM_isb 13.2 ns 13.2 ns 52993304 AWS Graviton (A-72) processor: BM_scalar_increment 0.897 ns 0.874 ns 801558633 BM_yield 0.877 ns 0.875 ns 800002377 BM_isb 13.0 ns 12.7 ns 55169412 Apple Arm64 M1 processor: BM_scalar_increment 0.315 ns 0.315 ns 1000000000 BM_yield 0.313 ns 0.313 ns 1000000000 BM_isb 9.06 ns 9.06 ns 77259282 static void BM_pause(benchmark::State& state) { for (auto _ : state) asm volatile("pause"::); } BENCHMARK(BM_pause); Intel Skylake processor: BM_scalar_increment 0.295 ns 0.295 ns 1000000000 BM_pause 41.7 ns 41.7 ns 16780553 Tested on Graviton2 aarch64-linux with `./x.py test`.
Reuse `sys::unix::cmath` on other platforms Reuse `sys::unix::cmath` on all non-`windows` platforms. `unix` is chosen as the canonical location instead of `unsupported` or `common` because `unsupported` doesn't make sense semantically and `common` is reserved for code that is supported on all platforms. Also `unix` is already the home of some non-`windows` code that is technically not exclusive to `unix` like `unix::path`.
…ulacrum Unignore a couple of tests
Be stricter about rejecting LLVM reserved registers in asm! LLVM will silently produce incorrect code if these registers are used as operands. cc ````@rust-lang/wg-inline-asm````
[Arm64] use isb instruction instead of yield in spin loops On arm64 we have seen on several databases that ISB (instruction synchronization barrier) is better to use than yield in a spin loop. The yield instruction is a nop. The isb instruction puts the processor to sleep for some short time. isb is a good equivalent to the pause instruction on x86. Below is an experiment that shows the effects of yield and isb on Arm64 and the time of a pause instruction on x86 Intel processors. The micro-benchmarks use https://github.com/google/benchmark.git ``` $ cat a.cc static void BM_scalar_increment(benchmark::State& state) { int i = 0; for (auto _ : state) benchmark::DoNotOptimize(i++); } BENCHMARK(BM_scalar_increment); static void BM_yield(benchmark::State& state) { for (auto _ : state) asm volatile("yield"::); } BENCHMARK(BM_yield); static void BM_isb(benchmark::State& state) { for (auto _ : state) asm volatile("isb"::); } BENCHMARK(BM_isb); BENCHMARK_MAIN(); $ g++ -o run a.cc -O2 -lbenchmark -lpthread $ ./run -------------------------------------------------------------- Benchmark Time CPU Iterations -------------------------------------------------------------- AWS Graviton2 (Neoverse-N1) processor: BM_scalar_increment 0.485 ns 0.485 ns 1000000000 BM_yield 0.400 ns 0.400 ns 1000000000 BM_isb 13.2 ns 13.2 ns 52993304 AWS Graviton (A-72) processor: BM_scalar_increment 0.897 ns 0.874 ns 801558633 BM_yield 0.877 ns 0.875 ns 800002377 BM_isb 13.0 ns 12.7 ns 55169412 Apple Arm64 M1 processor: BM_scalar_increment 0.315 ns 0.315 ns 1000000000 BM_yield 0.313 ns 0.313 ns 1000000000 BM_isb 9.06 ns 9.06 ns 77259282 ``` ``` static void BM_pause(benchmark::State& state) { for (auto _ : state) asm volatile("pause"::); } BENCHMARK(BM_pause); Intel Skylake processor: BM_scalar_increment 0.295 ns 0.295 ns 1000000000 BM_pause 41.7 ns 41.7 ns 16780553 ``` Tested on Graviton2 aarch64-linux with `./x.py test`.
Dylan-DPC-zz
commented
Apr 30, 2021
Author
@bors r+ rollup=never p=5 |
bors
commented
Apr 30, 2021
Collaborator
📌 Commit 7a1462f has been approved by |
bors
commented
Apr 30, 2021
Collaborator
⌛ Testing commit 7a1462f with merge 4a07567b863f1b1bf0d2d7341f366ce6778ba8e4... |
rust-log-analyzer
commented
Apr 30, 2021
Collaborator
The job Click to see the possible cause of the failure (guessed by this bot) |
bors
commented
Apr 30, 2021
Collaborator
💔 Test failed - checks-actions |
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for freeto join this conversation on GitHub.
Already have an account?
Sign in to comment
9 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Successful merges:
sys::unix::cmathon other platforms #84522 (Reusesys::unix::cmathon other platforms)Failed merges:
r? @ghost
@rustbot modify labels: rollup
Create a similar rollup