kselftest/arm64: Add pidbench for floating point syscall cases

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>
Link: https://lore.kernel.org/r/20211202165107.1075259-1-broonie@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/tools/testing/selftests/arm64/fp/.gitignore b/tools/testing/selftests/arm64/fp/.gitignore
index b67395903b9bbfb7b2fb7e928e0940ec71c30832..c50d86331ed2fbec7c0e9259d32a938e7e01df7b 100644 (file)
--- 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 ba1488c7c3153010a66e1d1aa4c737fbe97858df..95f0b877a060ba01db39165e659047a7429d8a0b 100644 (file)
--- 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 (file)
index 0000000..16a4363
--- /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