linux-kernel - [PATCH] selftests: vDSO: Build vDSO tests with O2 optimisation

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Message-ID: <46efa1f62e1604c98d10a1b6856a2b2aec0cfe9c.1725211324.git.christophe.leroy@csgroup.eu>
Date: Sun,  1 Sep 2024 19:24:03 +0200
From: Christophe Leroy <christophe.leroy@...roup.eu>
To: Shuah Khan <shuah@...nel.org>,
	"Jason A . Donenfeld" <Jason@...c4.com>
Cc: Christophe Leroy <christophe.leroy@...roup.eu>,
	linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org,
	linux-kselftest@...r.kernel.org
Subject: [PATCH] selftests: vDSO: Build vDSO tests with O2 optimisation

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@...roup.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