selftests: vDSO: Build vDSO tests with O2 optimisation

[PATCH] selftests: vDSO: Build vDSO tests with O2 optimisation

Posted by Christophe Leroy 1 year, 3 months ago

Without -O2, the generated code for testing chacha function is awful.
GCC even implements rol32() as a function instead of just using the
rotlwi instruction, that function is 20 instructions long.

	~# time ./vdso_test_chacha
	TAP version 13
	1..1
	ok 1 chacha: PASS
	real    0m 37.16s
	user    0m 36.89s
	sys     0m 0.26s

Several other selftests directory add -O2, and the kernel is also
always built with optimisation active. Do the same for vDSO selftests.

With this patch the time is reduced by approx 15%.

	~# time ./vdso_test_chacha
	TAP version 13
	1..1
	ok 1 chacha: PASS
	real    0m 32.09s
	user    0m 31.86s
	sys     0m 0.22s

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
 tools/testing/selftests/vDSO/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/vDSO/Makefile b/tools/testing/selftests/vDSO/Makefile
index cfb7c281b22c..96f25aa2f84e 100644
--- a/tools/testing/selftests/vDSO/Makefile
+++ b/tools/testing/selftests/vDSO/Makefile
@@ -13,7 +13,7 @@ TEST_GEN_PROGS += vdso_test_correctness
 TEST_GEN_PROGS += vdso_test_getrandom
 TEST_GEN_PROGS += vdso_test_chacha
 
-CFLAGS := -std=gnu99
+CFLAGS := -std=gnu99 -O2
 
 ifeq ($(CONFIG_X86_32),y)
 LDLIBS += -lgcc_s
-- 
2.44.0

Re: [PATCH] selftests: vDSO: Build vDSO tests with O2 optimisation

Posted by Jason A. Donenfeld 1 year, 3 months ago

On Sun, Sep 01, 2024 at 07:24:03PM +0200, Christophe Leroy wrote:
> Without -O2, the generated code for testing chacha function is awful.
> GCC even implements rol32() as a function instead of just using the
> rotlwi instruction, that function is 20 instructions long.
> 
> 	~# time ./vdso_test_chacha
> 	TAP version 13
> 	1..1
> 	ok 1 chacha: PASS
> 	real    0m 37.16s
> 	user    0m 36.89s
> 	sys     0m 0.26s
> 
> Several other selftests directory add -O2, and the kernel is also
> always built with optimisation active. Do the same for vDSO selftests.
> 
> With this patch the time is reduced by approx 15%.
> 
> 	~# time ./vdso_test_chacha
> 	TAP version 13
> 	1..1
> 	ok 1 chacha: PASS
> 	real    0m 32.09s
> 	user    0m 31.86s
> 	sys     0m 0.22s
> 

Seems reasonable. I'll queue it up.

Thanks.

Jason