ia64: VIRT_CPU_ACCOUNTING (accurate cpu time accounting)

This is last patch for check point building.

- kernel exit (stack switching from kernel to user)

In contrast, there is only one codes that switches stack from kernel to user. It is ia64_leave_kernel().

Following patch builds check point on this exit, including fetching ar.itc, cumulate cycles for stime and stamp updating.

Thanks,
H.Seto

---
 arch/ia64/kernel/entry.S |   20 ++++++++++++++++++++
 1 files changed, 20 insertions(+)

Index: linux-2.6.23/arch/ia64/kernel/entry.S =================================--- linux-2.6.23.orig/arch/ia64/kernel/entry.S +++ linux-2.6.23/arch/ia64/kernel/entry.S
@@ -995,6 +995,26 @@
shladd in0=loc1,3,r17
mov in1=0
;;
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING
+account_sys_leave:
+ alloc loc0=ar.pfs,2,7,0,0 // keep in0,in1
+ mov loc1=IA64_KR(CURRENT) // M2 (12 cycle read latency)
+ mov loc6=ar.itc
+ ;;
+ add loc2=TI_AC_STAMP+IA64_TASK_SIZE,loc1
+ add loc3=TI_AC_STIME+IA64_TASK_SIZE,loc1
+ ;;
+ ld8 loc4=[loc2] // get last stamp
+ ld8 loc5=[loc3] // cumulated stime
+ ;;
+ sub loc4=loc6,loc4 // elapsed time
+ ;;
+ add loc5=loc5,loc4 // sum
+ ;;
+ st8 [loc2]=loc6 // update stamp
+ st8 [loc3]=loc5 // update stime
+ ;;
+#endif
TEXT_ALIGN(32)
rse_clear_invalid:
#ifdef CONFIG_ITANIUM