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Message-Id: <20190206001107.16488-32-dima@arista.com>
Date: Wed, 6 Feb 2019 00:11:05 +0000
From: Dmitry Safonov <dima@...sta.com>
To: linux-kernel@...r.kernel.org
Cc: Andrei Vagin <avagin@...il.com>, Dmitry Safonov <dima@...sta.com>,
Adrian Reber <adrian@...as.de>,
Andrei Vagin <avagin@...nvz.org>,
Andy Lutomirski <luto@...nel.org>,
Andy Tucker <agtucker@...gle.com>,
Arnd Bergmann <arnd@...db.de>,
Christian Brauner <christian.brauner@...ntu.com>,
Cyrill Gorcunov <gorcunov@...nvz.org>,
Dmitry Safonov <0x7f454c46@...il.com>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
Jeff Dike <jdike@...toit.com>, Oleg Nesterov <oleg@...hat.com>,
Pavel Emelyanov <xemul@...tuozzo.com>,
Shuah Khan <shuah@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
containers@...ts.linux-foundation.org, criu@...nvz.org,
linux-api@...r.kernel.org, x86@...nel.org
Subject: [PATCH 31/32] x86/vdso: Align VDSO functions by CPU L1 cache line
From: Andrei Vagin <avagin@...il.com>
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 <dima@...sta.com>
Signed-off-by: Andrei Vagin <avagin@...il.com>
Signed-off-by: Dmitry Safonov <dima@...sta.com>
---
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
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