[GIT PULL] x86/asm changes for v4.13

[GIT PULL] x86/asm changes for v4.13

[Ingo Molnar]

Linus,

Please pull the latest x86-asm-for-linus git tree from:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86-asm-for-linus

   # HEAD: 236222d39347e0e486010f10c1493e83dbbdfba8 x86/uaccess: Optimize copy_user_enhanced_fast_string() for short strings

A single commit micro-optimizing short string copies on certain Intel CPUs.

 Thanks,

	Ingo

------------------>
Paolo Abeni (1):
      x86/uaccess: Optimize copy_user_enhanced_fast_string() for short strings


 arch/x86/lib/copy_user_64.S | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/lib/copy_user_64.S b/arch/x86/lib/copy_user_64.S
index c5959576c315..020f75cc8cf6 100644
--- a/arch/x86/lib/copy_user_64.S
+++ b/arch/x86/lib/copy_user_64.S
@@ -37,7 +37,7 @@ ENTRY(copy_user_generic_unrolled)
 	movl %edx,%ecx
 	andl $63,%edx
 	shrl $6,%ecx
-	jz 17f
+	jz .L_copy_short_string
 1:	movq (%rsi),%r8
 2:	movq 1*8(%rsi),%r9
 3:	movq 2*8(%rsi),%r10
@@ -58,7 +58,8 @@ ENTRY(copy_user_generic_unrolled)
 	leaq 64(%rdi),%rdi
 	decl %ecx
 	jnz 1b
-17:	movl %edx,%ecx
+.L_copy_short_string:
+	movl %edx,%ecx
 	andl $7,%edx
 	shrl $3,%ecx
 	jz 20f
@@ -174,6 +175,8 @@ EXPORT_SYMBOL(copy_user_generic_string)
  */
 ENTRY(copy_user_enhanced_fast_string)
 	ASM_STAC
+	cmpl $64,%edx
+	jb .L_copy_short_string	/* less then 64 bytes, avoid the costly 'rep' */
 	movl %edx,%ecx
 1:	rep
 	movsb

Re: [GIT PULL] x86/asm changes for v4.13

[Linus Torvalds]

On Mon, Jul 3, 2017 at 1:50 AM, Ingo Molnar <mingo@kernel.org> wrote:
>
> A single commit micro-optimizing short string copies on certain Intel CPUs.

That's slightly misleading - it's not string copies, it's just regular
user copies using the "fast string" interface.

Fixing that up in my merge commit message.

           Linus

Re: [GIT PULL] x86/asm changes for v4.13

[Ingo Molnar]

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Mon, Jul 3, 2017 at 1:50 AM, Ingo Molnar <mingo@kernel.org> wrote:
> >
> > A single commit micro-optimizing short string copies on certain Intel CPUs.
> 
> That's slightly misleading - it's not string copies, it's just regular
> user copies using the "fast string" interface.

Indeed!

> Fixing that up in my merge commit message.

Thanks!

	Ingo