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 <alicer...@google.com>
Suggested-by: Yury Norov [NVIDIA] <yury.no...@gmail.com>
Reviewed-by: Yury Norov [NVIDIA] <yury.no...@gmail.com>
Reviewed-by: Alice Ryhl <alicer...@google.com>
Signed-off-by: Burak Emir <b...@google.com>
---
MAINTAINERS | 1 +
lib/Kconfig.debug | 13 ++++
lib/Makefile | 1 +
lib/find_bit_benchmark_rust.rs | 104 ++++++++++++++++++++++++++++++++
rust/bindings/bindings_helper.h | 1 +
rust/kernel/bitmap.rs | 15 +++++
6 files changed, 135 insertions(+)
create mode 100644 lib/find_bit_benchmark_rust.rs
diff --git a/MAINTAINERS b/MAINTAINERS
index b2cef0e9c256..444aa282b8cd 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4307,6 +4307,7 @@ M: Alice Ryhl <alicer...@google.com>
M: Burak Emir <b...@google.com>
R: Yury Norov <yury.no...@gmail.com>
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 dc0e0c6ed075..386232d81a0e 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 392ff808c9b9..96a83b937a60 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 000000000000..6bdc51de2f30
--- /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::<Monotonic>::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::<Monotonic>::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<Self> {
+ 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 <b...@google.com>"],
+ 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 7bb575043c86..5d58316f871e 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -67,6 +67,7 @@
#include <linux/pm_opp.h>
#include <linux/poll.h>
#include <linux/property.h>
+#include <linux/random.h>
#include <linux/refcount.h>
#include <linux/regulator/consumer.h>
#include <linux/sched.h>
diff --git a/rust/kernel/bitmap.rs b/rust/kernel/bitmap.rs
index 9235808dc03c..6e0824579781 100644
--- a/rust/kernel/bitmap.rs
+++ b/rust/kernel/bitmap.rs
@@ -252,6 +252,21 @@ pub fn new(nbits: usize, flags: Flags) -> Result<Self,
AllocError> {
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::<ffi::c_void>(),
+ usize::div_ceil(self.nbits, bindings::BITS_PER_LONG as usize)
+ * bindings::BITS_PER_LONG as usize
+ / 8,
+ );
+ }
+ }
}
impl Bitmap {
--
2.51.0.355.g5224444f11-goog
