From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dmitry Safonov Subject: [PATCH 31/32] x86/vdso: Align VDSO functions by CPU L1 cache line Date: Wed, 6 Feb 2019 00:11:05 +0000 Message-ID: <20190206001107.16488-32-dima@arista.com> References: <20190206001107.16488-1-dima@arista.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20190206001107.16488-1-dima@arista.com> Sender: linux-kernel-owner@vger.kernel.org To: linux-kernel@vger.kernel.org Cc: Andrei Vagin , Dmitry Safonov , Adrian Reber , Andrei Vagin , Andy Lutomirski , Andy Tucker , Arnd Bergmann , Christian Brauner , Cyrill Gorcunov , Dmitry Safonov <0x7f454c46@gmail.com>, "Eric W. Biederman" , "H. Peter Anvin" , Ingo Molnar , Jeff Dike , Oleg Nesterov , Pavel Emelyanov , Shuah Khan , Thomas Gleixner , containers@lists.linux-foundation.org, criu@openvz.org, linux-api@vger.kernel.org, x86@kernel.org List-Id: linux-api@vger.kernel.org From: Andrei Vagin After performance testing VDSO patches a noticeable 20% regression was found on gettime_perf selftest with a cold cache. As it turns to be, before time namespaces introduction, VDSO functions were quite aligned to cache lines, but adding a new code to adjust timens offset inside namespace created a small shift and vdso functions become unaligned on cache lines. Add align to vdso functions with gcc option to fix performance drop. Coping the resulting numbers from cover letter: Hot CPU cache (more gettime_perf.c cycles - the better): | before | CONFIG_TIME_NS=n | host | inside timens --------|------------|------------------|-------------|------------- cycles | 139887013 | 139453003 | 139899785 | 128792458 diff (%)| 100 | 99.7 | 100 | 92 Cold cache (lesser tsc per gettime_perf_cold.c cycle - the better): | before | CONFIG_TIME_NS=n | host | inside timens --------|------------|------------------|-------------|------------- tsc | 6748 | 6718 | 6862 | 12682 diff (%)| 100 | 99.6 | 101.7 | 188 Measured on Intel(R) Core(TM) i5-6300U CPU @ 2.40GHz Co-developed-by: Dmitry Safonov Signed-off-by: Andrei Vagin Signed-off-by: Dmitry Safonov --- arch/x86/entry/vdso/Makefile | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile index 4e1659619e7e..2cac4660db05 100644 --- a/arch/x86/entry/vdso/Makefile +++ b/arch/x86/entry/vdso/Makefile @@ -4,6 +4,7 @@ # KBUILD_CFLAGS += $(DISABLE_LTO) -ffunction-sections +KBUILD_CFLAGS += -falign-functions=$(CONFIG_X86_L1_CACHE_SHIFT) KASAN_SANITIZE := n UBSAN_SANITIZE := n OBJECT_FILES_NON_STANDARD := y -- 2.20.1