ia64: On return from syscall, hint b7 with __kernel_syscall_via_epc().
Why is this a good idea? Clearing b7 to 0 is guaranteed to do us no
good and writing it with __kernel_syscall_via_epc() yields a 6 cycle
improvement _if_ the application performs another EPC-based system-
call without overwriting b7, which is not all that uncommon. Well
worth the minimal cost of 1 bundle of code.
Signed-off-by: David Mosberger-Tang <[EMAIL PROTECTED]>
diff -Nru a/arch/ia64/kernel/entry.S b/arch/ia64/kernel/entry.S
--- a/arch/ia64/kernel/entry.S 2005-03-23 13:28:12 -08:00
+++ b/arch/ia64/kernel/entry.S 2005-03-23 13:28:12 -08:00
@@ -692,7 +692,7 @@
;;
(p6) ld4 r31=[r18] // load
current_thread_info()->flags
ld8 r19=[r2],PT(B6)-PT(LOADRS) // load ar.rsc value for
"loadrs"
- mov b7=r0 // clear b7
+ nop.i 0
;;
ld8 r23=[r3],PT(R11)-PT(AR_BSPSTORE) // load ar.bspstore (may be
garbage)
ld8 r18=[r2],PT(R9)-PT(B6) // load b6
@@ -754,7 +754,14 @@
(pUStk) ld4 r17=[r3] // r17 = cpu_data->phys_stacked_size_p8
mov.m ar.csd=r0 // M2 clear ar.csd
mov f10=f0 // clear f10
+
+ nop.m 0
+ movl r14=__kernel_syscall_via_epc // X
;;
+ nop.m 0
+ nop.m 0
+ mov b7=r14 // I0 clear b7 (hint with
__kernel_syscall_via_epc)
+
mov r14=r0 // clear r14
mov f11=f0 // clear f11
(pKStk) br.cond.dpnt.many skip_rbs_switch
-
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