[IA64] speed up syscall path a bit more
Recently I noticed that clearing ar.ssd/ar.csd right before srlz.d is
causing significant stalling in the syscall path. The patch below
fixes that by moving the register-writes after srlz.d. On a Madison,
this drops break-based getpid() from 241 to 226 cycles (-15 cycles).
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/entry.S b/arch/ia64/kernel/entry.S
index 0272c01..73e23da 100644
--- a/arch/ia64/kernel/entry.S
+++ b/arch/ia64/kernel/entry.S
@@ -728,12 +728,8 @@
mov f8=f0 // clear f8
;;
ld8 r30=[r2],16 // M0|1 load cr.ifs
- mov.m ar.ssd=r0 // M2 clear ar.ssd
- cmp.eq p9,p0=r0,r0 // set p9 to indicate that we should restore cr.ifs
- ;;
ld8 r25=[r3],16 // M0|1 load ar.unat
- mov.m ar.csd=r0 // M2 clear ar.csd
- mov r22=r0 // clear r22
+ cmp.eq p9,p0=r0,r0 // set p9 to indicate that we should restore cr.ifs
;;
ld8 r26=[r2],PT(B0)-PT(AR_PFS) // M0|1 load ar.pfs
(pKStk) mov r22=psr // M2 read PSR now that interrupts are disabled
@@ -756,11 +752,15 @@
mov f7=f0 // clear f7
;;
ld8.fill r12=[r2] // restore r12 (sp)
+ mov.m ar.ssd=r0 // M2 clear ar.ssd
+ mov r22=r0 // clear r22
+
ld8.fill r15=[r3] // restore r15
+(pUStk) st1 [r14]=r17
addl r3=THIS_CPU(ia64_phys_stacked_size_p8),r0
;;
(pUStk) ld4 r3=[r3] // r3 = cpu_data->phys_stacked_size_p8
-(pUStk) st1 [r14]=r17
+ mov.m ar.csd=r0 // M2 clear ar.csd
mov b6=r18 // I0 restore b6
;;
mov r14=r0 // clear r14
