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 <an...@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;
--
_______________________________________________
Linuxppc-dev mailing list
Linuxppc-dev@lists.ozlabs.org
https://lists.ozlabs.org/listinfo/linuxppc-dev
