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powerpc: Move 64bit VDSO to improve context switch performance

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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>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
This commit is contained in:
Anton Blanchard 2009-07-13 20:53:51 +00:00 committed by Benjamin Herrenschmidt
parent 0d2d3e38f7
commit 30d0b36828
2 changed files with 7 additions and 3 deletions
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3
arch/powerpc/include/asm/vdso.h
View File

@ -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

7
arch/powerpc/kernel/vdso.c
View File

@ -203,7 +203,12 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
} 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;