[IA64] In syscall-entry, use st8 instead of stf8 to clear pt_regs.r8

Using stf8 seemed like a clever idea at the time, but stf8 forces
the cache-line to be invalidated in the L1D (if it happens to be
there already).  This patch eliminates a guaranteed L1D cache-miss
and, by itself, is good for a 1-2 cycle improvement for heavy-weight
syscalls.

Signed-off-by: David Mosberger-Tang <davidm@hpl.hp.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

diff --git a/arch/ia64/kernel/ivt.S b/arch/ia64/kernel/ivt.S
index d9c05d53435bd1d541538494336cffcc65df83c4..dc78c356ddd0e45bfd8e6e05b42be9f0eb2b8d68 100644 (file)
--- a/arch/ia64/kernel/ivt.S
+++ b/arch/ia64/kernel/ivt.S
@@ -1,7 +1,7 @@
 /*
  * arch/ia64/kernel/ivt.S
  *
- * Copyright (C) 1998-2001, 2003 Hewlett-Packard Co
+ * Copyright (C) 1998-2001, 2003, 2005 Hewlett-Packard Co
  *     Stephane Eranian <eranian@hpl.hp.com>
  *     David Mosberger <davidm@hpl.hp.com>
  * Copyright (C) 2000, 2002-2003 Intel Co
@@ -918,7 +918,7 @@ GLOBAL_ENTRY(ia64_syscall_setup)
        tnat.nz p14,p0=in6
        cmp.lt p10,p9=r11,r8    // frame size can't be more than local+8
        ;;
-       stf8 [r16]=f1           // ensure pt_regs.r8 != 0 (see handle_syscall_error)
+       mov r8=1
 (p9)   tnat.nz p10,p0=r15
        adds r12=-16,r1         // switch to kernel memory stack (with 16 bytes of scratch)
 
@@ -929,9 +929,9 @@ GLOBAL_ENTRY(ia64_syscall_setup)
        mov r13=r2                              // establish `current'
        movl r1=__gp                            // establish kernel global pointer
        ;;
+       st8 [r16]=r8            // ensure pt_regs.r8 != 0 (see handle_syscall_error)
 (p14)  mov in6=-1
 (p8)   mov in7=-1
-       nop.i 0
 
        cmp.eq pSys,pNonSys=r0,r0               // set pSys=1, pNonSys=0
        movl r17=FPSR_DEFAULT