x86: fix incorrect __read_mostly on _boot_cpu_pda

commit 26799a63110dcbe81291ea53178f6b4810d07424 upstream.

The pda rework (commit 3461b0af025251bbc6b3d56c821c6ac2de6f7209)
to remove static boot cpu pdas introduced a performance bug.

_boot_cpu_pda is the actual pda used by the boot cpu and is definitely
not "__read_mostly" and ended up polluting the read mostly section with
writes.  This bug caused regression of about 8-10% on certain syscall
intensive workloads.

Signed-off-by: Ravikiran Thirumalai <kiran@scalex86.org>
Acked-by: Mike Travis <travis@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index d16084f90649181e6e944e104118f7ec5de6a0e3..9461dc3d243cd5aad5075c600b7142ae1121dc80 100644 (file)
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -26,7 +26,7 @@
 #include <asm/bios_ebda.h>
 
 /* boot cpu pda */
-static struct x8664_pda _boot_cpu_pda __read_mostly;
+static struct x8664_pda _boot_cpu_pda;
 
 #ifdef CONFIG_SMP
 /*