kernel_optimize_test/arch/powerpc/lib/vmx-helper.c
Anton Blanchard fde69282b7 powerpc: POWER7 optimised copy_page using VMX and enhanced prefetch
Implement a POWER7 optimised copy_page using VMX and enhanced
prefetch instructions. We use enhanced prefetch hints to prefetch
both the load and store side. We copy a cacheline at a time and
fall back to regular loads and stores if we are unable to use VMX
(eg we are in an interrupt).

The following microbenchmark was used to assess the impact of
the patch:

http://ozlabs.org/~anton/junkcode/page_fault_file.c

We test MAP_PRIVATE page faults across a 1GB file, 100 times:

# time ./page_fault_file -p -l 1G -i 100

Before: 22.25s
After:  18.89s

17% faster

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
2012-07-03 14:14:44 +10:00

75 lines
1.9 KiB
C

/*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
* Copyright (C) IBM Corporation, 2011
*
* Authors: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
* Anton Blanchard <anton@au.ibm.com>
*/
#include <linux/uaccess.h>
#include <linux/hardirq.h>
#include <asm/switch_to.h>
int enter_vmx_usercopy(void)
{
if (in_interrupt())
return 0;
/* This acts as preempt_disable() as well and will make
* enable_kernel_altivec(). We need to disable page faults
* as they can call schedule and thus make us lose the VMX
* context. So on page faults, we just fail which will cause
* a fallback to the normal non-vmx copy.
*/
pagefault_disable();
enable_kernel_altivec();
return 1;
}
/*
* This function must return 0 because we tail call optimise when calling
* from __copy_tofrom_user_power7 which returns 0 on success.
*/
int exit_vmx_usercopy(void)
{
pagefault_enable();
return 0;
}
int enter_vmx_copy(void)
{
if (in_interrupt())
return 0;
preempt_disable();
enable_kernel_altivec();
return 1;
}
/*
* All calls to this function will be optimised into tail calls. We are
* passed a pointer to the destination which we return as required by a
* memcpy implementation.
*/
void *exit_vmx_copy(void *dest)
{
preempt_enable();
return dest;
}