From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [203.10.76.45]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "mx.ozlabs.org", Issuer "CA Cert Signing Authority" (verified OK)) by bilbo.ozlabs.org (Postfix) with ESMTPS id CBFCCB7092 for ; Tue, 14 Jul 2009 17:00:47 +1000 (EST) Received: from bilbo.ozlabs.org (bilbo.ozlabs.org [203.10.76.25]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "bilbo.ozlabs.org", Issuer "CAcert Class 3 Root" (verified OK)) by ozlabs.org (Postfix) with ESMTPS id 95D94DDDB6 for ; Tue, 14 Jul 2009 17:00:47 +1000 (EST) Message-Id: <20090714065425.301516312@samba.org> References: <20090714065350.659537380@samba.org> Date: Tue, 14 Jul 2009 16:53:51 +1000 From: Anton Blanchard To: benh@kernel.crashing.org Subject: [patch 1/3] powerpc: Move 64bit VDSO to improve context switch performance Cc: linuxppc-dev@ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 --- 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; --