linux/arch/ia64
Chen, Kenneth W a0776ec8e9 [IA64] remove per-cpu ia64_phys_stacked_size_p8
It's not efficient to use a per-cpu variable just to store
how many physical stack register a cpu has.  Ever since the
incarnation of ia64 up till upcoming Montecito processor, that
variable has "glued" to 96. Having a variable in memory means
that the kernel is burning an extra cacheline access on every
syscall and kernel exit path.  Such "static" value is better
served with the instruction patching utility exists today.
Convert ia64_phys_stacked_size_p8 into dynamic insn patching.

This also has a pleasant side effect of eliminating access to
per-cpu area while psr.ic=0 in the kernel exit path. (fixable
for per-cpu DTC work, but why bother?)

There are some concerns with the default value that the instruc-
tion encoded in the kernel image.  It shouldn't be concerned.
The reasons are:

(1) cpu_init() is called at CPU initialization.  In there, we
    find out physical stack register size from PAL and patch
    two instructions in kernel exit code.  The code in question
    can not be executed before the patching is done.

(2) current implementation stores zero in ia64_phys_stacked_size_p8,
    and that's what the current kernel exit path loads the value with.
    With the new code, it is equivalent that we store reg size 96
    in ia64_phys_stacked_size_p8, thus creating a better safety net.
    Given (1) above can never fail, having (2) is just a bonus.

All in all, this patch allow one less memory reference in the kernel
exit path, thus reducing syscall and interrupt return latency; and
avoid polluting potential useful data in the CPU cache.

Signed-off-by: Ken Chen <kenneth.w.chen@intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>
2007-02-06 15:04:18 -08:00
..
configs [IA64] update sn2_defconfig 2006-10-17 14:55:45 -07:00
dig [PATCH] tty: Remove include of screen_info.h from tty.h 2006-07-10 13:24:16 -07:00
hp [IA64] s/termios/ktermios/ in simserial.c 2006-12-12 10:47:36 -08:00
ia32 [PATCH] struct path: convert ia64 2006-12-08 08:28:45 -08:00
kernel [IA64] remove per-cpu ia64_phys_stacked_size_p8 2007-02-06 15:04:18 -08:00
lib [IA64] tidy up return value of ip_fast_csum 2006-12-07 11:19:59 -08:00
mm [PATCH] Fix sparsemem on Cell 2007-01-11 18:18:20 -08:00
oprofile Remove obsolete #include <linux/config.h> 2006-06-30 19:25:36 +02:00
pci [IA64] replace kmalloc+memset with kzalloc 2006-12-07 13:46:43 -08:00
scripts Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
sn ACPI: Altix: ACPI _PRT support 2007-01-04 12:18:19 -05:00
defconfig [PATCH] sgiioc4: Always share IRQ 2006-07-31 13:28:40 -07:00
install.sh Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
Kconfig [PATCH] LOG2: Implement a general integer log2 facility in the kernel 2006-12-08 08:28:51 -08:00
Kconfig.debug [PATCH] Move Kprobes and Oprofile to "Instrumentation Support" menu 2005-11-07 07:53:35 -08:00
Makefile [IA64] add vmlinuz target 2006-06-21 14:31:07 -07:00
module.lds Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00