From: Burak Emir Date: Mon, 8 Sep 2025 07:21:54 +0000 (+0000) Subject: rust: add find_bit_benchmark_rust module. X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=38cc91db2e87ab55bfca2b194e791867b77f9e55;p=thirdparty%2Fkernel%2Fstable.git rust: add find_bit_benchmark_rust module. Microbenchmark protected by a config FIND_BIT_BENCHMARK_RUST, following `find_bit_benchmark.c` but testing the Rust Bitmap API. We add a fill_random() method protected by the config in order to maintain the abstraction. The sample output from the benchmark, both C and Rust version: find_bit_benchmark.c output: ``` Start testing find_bit() with random-filled bitmap [ 438.101937] find_next_bit: 860188 ns, 163419 iterations [ 438.109471] find_next_zero_bit: 912342 ns, 164262 iterations [ 438.116820] find_last_bit: 726003 ns, 163419 iterations [ 438.130509] find_nth_bit: 7056993 ns, 16269 iterations [ 438.139099] find_first_bit: 1963272 ns, 16270 iterations [ 438.173043] find_first_and_bit: 27314224 ns, 32654 iterations [ 438.180065] find_next_and_bit: 398752 ns, 73705 iterations [ 438.186689] Start testing find_bit() with sparse bitmap [ 438.193375] find_next_bit: 9675 ns, 656 iterations [ 438.201765] find_next_zero_bit: 1766136 ns, 327025 iterations [ 438.208429] find_last_bit: 9017 ns, 656 iterations [ 438.217816] find_nth_bit: 2749742 ns, 655 iterations [ 438.225168] find_first_bit: 721799 ns, 656 iterations [ 438.231797] find_first_and_bit: 2819 ns, 1 iterations [ 438.238441] find_next_and_bit: 3159 ns, 1 iterations ``` find_bit_benchmark_rust.rs output: ``` [ 451.182459] find_bit_benchmark_rust: [ 451.186688] Start testing find_bit() Rust with random-filled bitmap [ 451.194450] next_bit: 777950 ns, 163644 iterations [ 451.201997] next_zero_bit: 918889 ns, 164036 iterations [ 451.208642] Start testing find_bit() Rust with sparse bitmap [ 451.214300] next_bit: 9181 ns, 654 iterations [ 451.222806] next_zero_bit: 1855504 ns, 327026 iterations ``` Here are the results from 32 samples, with 95% confidence interval. The microbenchmark was built with RUST_BITMAP_HARDENED=n and run on a machine that did not execute other processes. Random-filled bitmap: +-----------+-------+-----------+--------------+-----------+-----------+ | Benchmark | Lang | Mean (ms) | Std Dev (ms) | 95% CI Lo | 95% CI Hi | +-----------+-------+-----------+--------------+-----------+-----------+ | find_bit/ | C | 825.07 | 53.89 | 806.40 | 843.74 | | next_bit | Rust | 870.91 | 46.29 | 854.88 | 886.95 | +-----------+-------+-----------+--------------+-----------+-----------+ | find_zero/| C | 933.56 | 56.34 | 914.04 | 953.08 | | next_zero | Rust | 945.85 | 60.44 | 924.91 | 966.79 | +-----------+-------+-----------+--------------+-----------+-----------+ Rust appears 5.5% slower for next_bit, 1.3% slower for next_zero. Sparse bitmap: +-----------+-------+-----------+--------------+-----------+-----------+ | Benchmark | Lang | Mean (ms) | Std Dev (ms) | 95% CI Lo | 95% CI Hi | +-----------+-------+-----------+--------------+-----------+-----------+ | find_bit/ | C | 13.17 | 6.21 | 11.01 | 15.32 | | next_bit | Rust | 14.30 | 8.27 | 11.43 | 17.17 | +-----------+-------+-----------+--------------+-----------+-----------+ | find_zero/| C | 1859.31 | 82.30 | 1830.80 | 1887.83 | | next_zero | Rust | 1908.09 | 139.82 | 1859.65 | 1956.54 | +-----------+-------+-----------+--------------+-----------+-----------+ Rust appears 8.5% slower for next_bit, 2.6% slower for next_zero. In summary, taking the arithmetic mean of all slow-downs, we can say the Rust API has a 4.5% slowdown. Suggested-by: Alice Ryhl Suggested-by: Yury Norov (NVIDIA) Reviewed-by: Yury Norov (NVIDIA) Reviewed-by: Alice Ryhl Signed-off-by: Burak Emir Signed-off-by: Yury Norov (NVIDIA) --- diff --git a/MAINTAINERS b/MAINTAINERS index d59bd6f8aef18..258ede14f4cc8 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -4307,6 +4307,7 @@ M: Alice Ryhl M: Burak Emir R: Yury Norov S: Maintained +F: lib/find_bit_benchmark_rust.rs F: rust/kernel/bitmap.rs BITOPS API diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index dc0e0c6ed075e..386232d81a0e3 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -2607,6 +2607,19 @@ config FIND_BIT_BENCHMARK If unsure, say N. +config FIND_BIT_BENCHMARK_RUST + tristate "Test find_bit functions in Rust" + depends on RUST + help + This builds the "find_bit_benchmark_rust" module. It is a micro + benchmark that measures the performance of Rust functions that + correspond to the find_*_bit() operations in C. It follows the + FIND_BIT_BENCHMARK closely but will in general not yield same + numbers due to extra bounds checks and overhead of foreign + function calls. + + If unsure, say N. + config TEST_FIRMWARE tristate "Test firmware loading via userspace interface" depends on FW_LOADER diff --git a/lib/Makefile b/lib/Makefile index 392ff808c9b90..96a83b937a605 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -62,6 +62,7 @@ obj-y += hexdump.o obj-$(CONFIG_TEST_HEXDUMP) += test_hexdump.o obj-y += kstrtox.o obj-$(CONFIG_FIND_BIT_BENCHMARK) += find_bit_benchmark.o +obj-$(CONFIG_FIND_BIT_BENCHMARK_RUST) += find_bit_benchmark_rust.o obj-$(CONFIG_TEST_BPF) += test_bpf.o test_dhry-objs := dhry_1.o dhry_2.o dhry_run.o obj-$(CONFIG_TEST_DHRY) += test_dhry.o diff --git a/lib/find_bit_benchmark_rust.rs b/lib/find_bit_benchmark_rust.rs new file mode 100644 index 0000000000000..6bdc51de2f307 --- /dev/null +++ b/lib/find_bit_benchmark_rust.rs @@ -0,0 +1,104 @@ +// SPDX-License-Identifier: GPL-2.0 +//! Benchmark for find_bit-like methods in Bitmap Rust API. + +use kernel::alloc::flags::GFP_KERNEL; +use kernel::bindings; +use kernel::bitmap::BitmapVec; +use kernel::error::{code, Result}; +use kernel::prelude::module; +use kernel::time::{Instant, Monotonic}; +use kernel::ThisModule; +use kernel::{pr_cont, pr_err}; + +const BITMAP_LEN: usize = 4096 * 8 * 10; +// Reciprocal of the fraction of bits that are set in sparse bitmap. +const SPARSENESS: usize = 500; + +/// Test module that benchmarks performance of traversing bitmaps. +struct Benchmark(); + +fn test_next_bit(bitmap: &BitmapVec) { + let time = Instant::::now(); + let mut cnt = 0; + let mut i = 0; + + while let Some(index) = bitmap.next_bit(i) { + cnt += 1; + i = index + 1; + // CONFIG_RUST_BITMAP_HARDENED enforces strict bounds. + if i == BITMAP_LEN { + break; + } + } + + let delta = time.elapsed(); + pr_cont!( + "\nnext_bit: {:18} ns, {:6} iterations", + delta.as_nanos(), + cnt + ); +} + +fn test_next_zero_bit(bitmap: &BitmapVec) { + let time = Instant::::now(); + let mut cnt = 0; + let mut i = 0; + + while let Some(index) = bitmap.next_zero_bit(i) { + cnt += 1; + i = index + 1; + // CONFIG_RUST_BITMAP_HARDENED enforces strict bounds. + if i == BITMAP_LEN { + break; + } + } + + let delta = time.elapsed(); + pr_cont!( + "\nnext_zero_bit: {:18} ns, {:6} iterations", + delta.as_nanos(), + cnt + ); +} + +fn find_bit_test() { + pr_err!("Benchmark"); + pr_cont!("\nStart testing find_bit() Rust with random-filled bitmap"); + + let mut bitmap = BitmapVec::new(BITMAP_LEN, GFP_KERNEL).expect("alloc bitmap failed"); + bitmap.fill_random(); + + test_next_bit(&bitmap); + test_next_zero_bit(&bitmap); + + pr_cont!("\nStart testing find_bit() Rust with sparse bitmap"); + + let mut bitmap = BitmapVec::new(BITMAP_LEN, GFP_KERNEL).expect("alloc sparse bitmap failed"); + let nbits = BITMAP_LEN / SPARSENESS; + for _i in 0..nbits { + // SAFETY: __get_random_u32_below is safe to call with any u32 argument. + let bit = + unsafe { bindings::__get_random_u32_below(BITMAP_LEN.try_into().unwrap()) as usize }; + bitmap.set_bit(bit); + } + + test_next_bit(&bitmap); + test_next_zero_bit(&bitmap); + pr_cont!("\n"); +} + +impl kernel::Module for Benchmark { + fn init(_module: &'static ThisModule) -> Result { + find_bit_test(); + // Return error so test module can be inserted again without rmmod. + Err(code::EINVAL) + } +} + +module! { + type: Benchmark, + name: "find_bit_benchmark_rust", + authors: ["Burak Emir "], + description: "Module with benchmark for bitmap Rust API", + license: "GPL v2", +} diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h index 7bb575043c862..5d58316f871ec 100644 --- a/rust/bindings/bindings_helper.h +++ b/rust/bindings/bindings_helper.h @@ -67,6 +67,7 @@ #include #include #include +#include #include #include #include diff --git a/rust/kernel/bitmap.rs b/rust/kernel/bitmap.rs index f349b1eb59f9b..f459156944542 100644 --- a/rust/kernel/bitmap.rs +++ b/rust/kernel/bitmap.rs @@ -252,6 +252,21 @@ impl BitmapVec { pub fn len(&self) -> usize { self.nbits } + + /// Fills this `Bitmap` with random bits. + #[cfg(CONFIG_FIND_BIT_BENCHMARK_RUST)] + pub fn fill_random(&mut self) { + // SAFETY: `self.as_mut_ptr` points to either an array of the + // appropriate length or one usize. + unsafe { + bindings::get_random_bytes( + self.as_mut_ptr().cast::(), + usize::div_ceil(self.nbits, bindings::BITS_PER_LONG as usize) + * bindings::BITS_PER_LONG as usize + / 8, + ); + } + } } impl Bitmap {