[IA64] VIRT_CPU_ACCOUNTING (accurate cpu time accounting)

This patch implements VIRT_CPU_ACCOUNTING for ia64,
which enable us to use more accurate cpu time accounting.

The VIRT_CPU_ACCOUNTING is an item of kernel config, which s390
and powerpc arch have.  By turning this config on, these archs
change the mechanism of cpu time accounting from tick-sampling
based one to state-transition based one.

The state-transition based accounting is done by checking time
(cycle counter in processor) at every state-transition point,
such as entrance/exit of kernel, interrupt, softirq etc.
The difference between point to point is the actual time consumed
during in the state. There is no doubt about that this value is
more accurate than that of tick-sampling based accounting.

Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/arch/ia64/kernel/head.S b/arch/ia64/kernel/head.S
index d3a41d5f8d12..ddeab4e36fd5 100644
--- a/arch/ia64/kernel/head.S
+++ b/arch/ia64/kernel/head.S
@@ -1002,6 +1002,26 @@ GLOBAL_ENTRY(sched_clock)
         br.ret.sptk.many rp
 END(sched_clock)
 
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING
+GLOBAL_ENTRY(cycle_to_cputime)
+        alloc r16=ar.pfs,1,0,0,0
+        addl r8=THIS_CPU(cpu_info) + IA64_CPUINFO_NSEC_PER_CYC_OFFSET,r0
+        ;;
+        ldf8 f8=[r8]
+        ;;
+        setf.sig f9=r32
+        ;;
+        xmpy.lu f10=f9,f8       // calculate low 64 bits of 128-bit product     (4 cyc)
+        xmpy.hu f11=f9,f8       // calculate high 64 bits of 128-bit product
+        ;;
+        getf.sig r8=f10         //                                              (5 cyc)
+        getf.sig r9=f11
+        ;;
+        shrp r8=r9,r8,IA64_NSEC_PER_CYC_SHIFT
+        br.ret.sptk.many rp
+END(cycle_to_cputime)
+#endif /* CONFIG_VIRT_CPU_ACCOUNTING */
+
 GLOBAL_ENTRY(start_kernel_thread)
         .prologue
         .save rp, r0                            // this is the end of the call-chain