From: Anton Blanchard <anton@samba.org>
To: benh@kernel.crashing.org
Cc: linuxppc-dev@ozlabs.org
Subject: [patch 1/3] powerpc: Move 64bit VDSO to improve context switch performance
Date: Tue, 14 Jul 2009 16:53:51 +1000 [thread overview]
Message-ID: <20090714065425.301516312@samba.org> (raw)
In-Reply-To: 20090714065350.659537380@samba.org
On 64bit applications the VDSO is the only thing in segment 0. Since the VDSO
is position independent we can remove the hint and let get_unmapped_area pick
an area. This will mean the vdso will be near other mmaps and will share
an SLB entry:
10000000-10001000 r-xp 00000000 08:06 5778459 /root/context_switch_64
10010000-10011000 r--p 00000000 08:06 5778459 /root/context_switch_64
10011000-10012000 rw-p 00001000 08:06 5778459 /root/context_switch_64
fffa92ae000-fffa92b0000 rw-p 00000000 00:00 0
fffa92b0000-fffa9453000 r-xp 00000000 08:06 4334051 /lib64/power6/libc-2.9.so
fffa9453000-fffa9462000 ---p 001a3000 08:06 4334051 /lib64/power6/libc-2.9.so
fffa9462000-fffa9466000 r--p 001a2000 08:06 4334051 /lib64/power6/libc-2.9.so
fffa9466000-fffa947c000 rw-p 001a6000 08:06 4334051 /lib64/power6/libc-2.9.so
fffa947c000-fffa9480000 rw-p 00000000 00:00 0
fffa9480000-fffa94a8000 r-xp 00000000 08:06 4333852 /lib64/ld-2.9.so
fffa94b3000-fffa94b4000 rw-p 00000000 00:00 0
fffa94b4000-fffa94b7000 r-xp 00000000 00:00 0 [vdso] <----- here I am
fffa94b7000-fffa94b8000 r--p 00027000 08:06 4333852 /lib64/ld-2.9.so
fffa94b8000-fffa94bb000 rw-p 00028000 08:06 4333852 /lib64/ld-2.9.so
fffa94bb000-fffa94bc000 rw-p 00000000 00:00 0
fffe4c10000-fffe4c25000 rw-p 00000000 00:00 0 [stack]
On a microbenchmark that bounces a token between two 64bit processes over pipes
and calls gettimeofday each iteration (to access the VDSO), our context switch
rate goes from 268k to 277k ctx switches/sec (tested on a 4GHz POWER6).
Signed-off-by: Anton Blanchard <anton@samba.org>
---
Index: linux.trees.git/arch/powerpc/include/asm/vdso.h
===================================================================
--- linux.trees.git.orig/arch/powerpc/include/asm/vdso.h 2009-07-14 11:41:52.000000000 +1000
+++ linux.trees.git/arch/powerpc/include/asm/vdso.h 2009-07-14 11:42:59.000000000 +1000
@@ -7,9 +7,8 @@
#define VDSO32_LBASE 0x100000
#define VDSO64_LBASE 0x100000
-/* Default map addresses */
+/* Default map addresses for 32bit vDSO */
#define VDSO32_MBASE VDSO32_LBASE
-#define VDSO64_MBASE VDSO64_LBASE
#define VDSO_VERSION_STRING LINUX_2.6.15
Index: linux.trees.git/arch/powerpc/kernel/vdso.c
===================================================================
--- linux.trees.git.orig/arch/powerpc/kernel/vdso.c 2009-07-14 11:41:46.000000000 +1000
+++ linux.trees.git/arch/powerpc/kernel/vdso.c 2009-07-14 12:03:13.000000000 +1000
@@ -203,7 +203,12 @@
} else {
vdso_pagelist = vdso64_pagelist;
vdso_pages = vdso64_pages;
- vdso_base = VDSO64_MBASE;
+ /*
+ * On 64bit we don't have a preferred map address. This
+ * allows get_unmapped_area to find an area near other mmaps
+ * and most likely share a SLB entry.
+ */
+ vdso_base = 0;
}
#else
vdso_pagelist = vdso32_pagelist;
--
next prev parent reply other threads:[~2009-07-14 7:00 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-07-14 6:53 [patch 0/3] PowerPC context switch optimisations Anton Blanchard
2009-07-14 6:53 ` Anton Blanchard [this message]
2009-07-14 7:07 ` [patch 1/3] powerpc: Move 64bit VDSO to improve context switch performance Benjamin Herrenschmidt
2009-07-14 7:38 ` Anton Blanchard
2009-10-02 19:14 ` Andreas Schwab
[not found] ` <m2ocophale.fsf__34527.2158309401$1254511503$gmane$org@igel.home>
2009-10-03 14:15 ` Andreas Schwab
2009-10-03 14:51 ` Andreas Schwab
2009-10-03 21:53 ` Benjamin Herrenschmidt
2009-10-04 12:35 ` Andreas Schwab
2009-07-14 6:53 ` [patch 2/3] powerpc: Rearrange SLB preload code Anton Blanchard
2009-07-14 6:53 ` [patch 3/3] powerpc: Preload application text segment instead of TASK_UNMAPPED_BASE Anton Blanchard
2009-07-14 7:10 ` Benjamin Herrenschmidt
2009-07-14 7:27 ` Anton Blanchard
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