From 53ee11ae0d73f28029a5f0d991bc4dcd7c817e7a Mon Sep 17 00:00:00 2001 From: Andi Kleen Date: Tue, 26 Sep 2006 10:52:38 +0200 Subject: [PATCH] Optimize PDA accesses slightly Based on a idea by Jeremy Fitzhardinge: Replace the volatiles and memory clobbers in the PDA access with telling gcc about access to a proxy PDA structure that doesn't actually exist. But the dummy accesses give a defined ordering for read/write accesses. Also add some memory barriers to the early GS initialization to make sure no PDA access is moved before it. Advantage is some .text savings (probably most from better code for accessing "current"): text data bss dec hex filename 4845647 1223688 615864 6685199 66020f vmlinux 4837780 1223688 615864 6677332 65e354 vmlinux-pda 1.2% smaller code Cc: Jeremy Fitzhardinge Signed-off-by: Andi Kleen --- arch/x86_64/kernel/setup64.c | 3 +++ 1 file changed, 3 insertions(+) (limited to 'arch') diff --git a/arch/x86_64/kernel/setup64.c b/arch/x86_64/kernel/setup64.c index e85cfbb49b63..491361752c70 100644 --- a/arch/x86_64/kernel/setup64.c +++ b/arch/x86_64/kernel/setup64.c @@ -121,7 +121,10 @@ void pda_init(int cpu) /* Setup up data that may be needed in __get_free_pages early */ asm volatile("movl %0,%%fs ; movl %0,%%gs" :: "r" (0)); + /* Memory clobbers used to order PDA accessed */ + mb(); wrmsrl(MSR_GS_BASE, pda); + mb(); pda->cpunumber = cpu; pda->irqcount = -1; -- cgit v1.2.2