Since it's likely to be useful for performance work with SVE let's have a pidbench that gives us some numbers for consideration. In order to ensure that we test exactly the scenario we want this is written in assembly - if system libraries use SVE this would stop us exercising the case where the process has never used SVE.

We exercise three cases:

- Never having used SVE. - Having used SVE once. - Using SVE after each syscall.

by spinning running getpid() for a fixed number of iterations with the time measured using CNTVCT_EL0 reported on the console. This is obviously a totally unrealistic benchmark which will show the extremes of any performance variation but equally given the potential gotchas with use of FP instructions by system libraries it's good to have some concrete code shared to make it easier to compare notes on results.

Testing over multiple SVE vector lengths will need to be done with vlset currently, the test could be extended to iterate over all of them if desired.

Signed-off-by: Mark Brown broonie@kernel.org --- tools/testing/selftests/arm64/fp/.gitignore | 1 + tools/testing/selftests/arm64/fp/Makefile | 4 +- .../testing/selftests/arm64/fp/fp-pidbench.S | 71 +++++++++++++++++++ 3 files changed, 75 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/arm64/fp/fp-pidbench.S

diff --git a/tools/testing/selftests/arm64/fp/.gitignore b/tools/testing/selftests/arm64/fp/.gitignore index b67395903b9b..c50d86331ed2 100644 --- a/tools/testing/selftests/arm64/fp/.gitignore +++ b/tools/testing/selftests/arm64/fp/.gitignore @@ -1,3 +1,4 @@ +fp-pidbench fpsimd-test rdvl-sve sve-probe-vls diff --git a/tools/testing/selftests/arm64/fp/Makefile b/tools/testing/selftests/arm64/fp/Makefile index ba1488c7c315..95f0b877a060 100644 --- a/tools/testing/selftests/arm64/fp/Makefile +++ b/tools/testing/selftests/arm64/fp/Makefile @@ -2,13 +2,15 @@

CFLAGS += -I../../../../../usr/include/ TEST_GEN_PROGS := sve-ptrace sve-probe-vls vec-syscfg -TEST_PROGS_EXTENDED := fpsimd-test fpsimd-stress \ +TEST_PROGS_EXTENDED := fp-pidbench fpsimd-test fpsimd-stress \ rdvl-sve \ sve-test sve-stress \ vlset

all: $(TEST_GEN_PROGS) $(TEST_PROGS_EXTENDED)

+fp-pidbench: fp-pidbench.S asm-utils.o + $(CC) -nostdlib $^ -o $@ fpsimd-test: fpsimd-test.o asm-utils.o $(CC) -nostdlib $^ -o $@ rdvl-sve: rdvl-sve.o rdvl.o diff --git a/tools/testing/selftests/arm64/fp/fp-pidbench.S b/tools/testing/selftests/arm64/fp/fp-pidbench.S new file mode 100644 index 000000000000..16a436389bfc --- /dev/null +++ b/tools/testing/selftests/arm64/fp/fp-pidbench.S @@ -0,0 +1,71 @@ +// SPDX-License-Identifier: GPL-2.0-only +// Copyright (C) 2021 ARM Limited. +// Original author: Mark Brown broonie@kernel.org +// +// Trivial syscall overhead benchmark. +// +// This is implemented in asm to ensure that we don't have any issues with +// system libraries using instructions that disrupt the test. + +#include <asm/unistd.h> +#include "assembler.h" + +.arch_extension sve + +.macro test_loop per_loop + mov x10, x20 + mov x8, #__NR_getpid + mrs x11, CNTVCT_EL0 +1: + \per_loop + svc #0 + sub x10, x10, #1 + cbnz x10, 1b + + mrs x12, CNTVCT_EL0 + sub x0, x12, x11 + bl putdec + puts "\n" +.endm + +// Main program entry point +.globl _start +function _start +_start: + puts "Iterations per test: " + mov x20, #10000 + lsl x20, x20, #8 + mov x0, x20 + bl putdec + puts "\n" + + // Test having never used SVE + puts "No SVE: " + test_loop + + // Check for SVE support - should use hwcap but that's hard in asm + mrs x0, ID_AA64PFR0_EL1 + ubfx x0, x0, #32, #4 + cbnz x0, 1f + puts "System does not support SVE\n" + b out +1: + + // Execute a SVE instruction + puts "SVE VL: " + rdvl x0, #8 + bl putdec + puts "\n" + + puts "SVE used once: " + test_loop + + // Use SVE per syscall + puts "SVE used per syscall: " + test_loop "rdvl x0, #8" + + // And we're done +out: + mov x0, #0 + mov x8, #__NR_exit + svc #0