Re: [PATCH v2 4/6] x86: Add clear_page_nocache
From: Jan Beulich <hidden>
Date: 2012-08-09 15:22:14
Also in:
linux-mips, linux-mm, linux-sh, lkml, sparclinux
quoted
quoted
On 09.08.12 at 17:03, "Kirill A. Shutemov" <kirill.shutemov@linux.intel=
.com> wrote:
From: Andi Kleen <redacted> =20 Add a cache avoiding version of clear_page. Straight forward integer =
variant
of the existing 64bit clear_page, for both 32bit and 64bit.
While on 64-bit this is fine, I fail to see how you avoid using the SSE2 instruction on non-SSE2 systems.
Also add the necessary glue for highmem including a layer that non cache coherent architectures that use the virtual address for flushing can hook in. This is not needed on x86 of course. =20 If an architecture wants to provide cache avoiding version of clear_page it should to define ARCH_HAS_USER_NOCACHE to 1 and implement clear_page_nocache() and clear_user_highpage_nocache(). =20 Signed-off-by: Andi Kleen <redacted> Signed-off-by: Kirill A. Shutemov <redacted> --- arch/x86/include/asm/page.h | 2 ++ arch/x86/include/asm/string_32.h | 5 +++++ arch/x86/include/asm/string_64.h | 5 +++++ arch/x86/lib/Makefile | 1 + arch/x86/lib/clear_page_nocache_32.S | 30 ++++++++++++++++++++++++++++=
++
arch/x86/lib/clear_page_nocache_64.S | 29 ++++++++++++++++++++++++++++=
+
Couldn't this more reasonably go into clear_page_{32,64}.S?
quoted hunk ↗ jump to hunk
arch/x86/mm/fault.c | 7 +++++++ 7 files changed, 79 insertions(+), 0 deletions(-) create mode 100644 arch/x86/lib/clear_page_nocache_32.S create mode 100644 arch/x86/lib/clear_page_nocache_64.S ...--- /dev/null +++ b/arch/x86/lib/clear_page_nocache_32.S@@ -0,0 +1,30 @@ +#include <linux/linkage.h> +#include <asm/dwarf2.h> + +/* + * Zero a page avoiding the caches + * rdi page
Wrong comment.
+ */ +ENTRY(clear_page_nocache) + CFI_STARTPROC + mov %eax,%edi
You need to pick a different register here (e.g. %edx), since %edi has to be preserved by all functions called from C.
+ xorl %eax,%eax + movl $4096/64,%ecx + .p2align 4 +.Lloop: + decl %ecx +#define PUT(x) movnti %eax,x*8(%edi) ; movnti %eax,x*8+4(%edi)
Is doing twice as much unrolling as on 64-bit really worth it? Jan