cputime: Generic on-demand virtual cputime accounting

If we want to stop the tick further idle, we need to be
able to account the cputime without using the tick.

Virtual based cputime accounting solves that problem by
hooking into kernel/user boundaries.

However implementing CONFIG_VIRT_CPU_ACCOUNTING require
low level hooks and involves more overhead. But we already
have a generic context tracking subsystem that is required
for RCU needs by archs which plan to shut down the tick
outside idle.

This patch implements a generic virtual based cputime
accounting that relies on these generic kernel/user hooks.

There are some upsides of doing this:

- This requires no arch code to implement CONFIG_VIRT_CPU_ACCOUNTING
if context tracking is already built (already necessary for RCU in full
tickless mode).

- We can rely on the generic context tracking subsystem to dynamically
(de)activate the hooks, so that we can switch anytime between virtual
and tick based accounting. This way we don't have the overhead
of the virtual accounting when the tick is running periodically.

And one downside:

- There is probably more overhead than a native virtual based cputime
accounting. But this relies on hooks that are already set anyway.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 8 insertions, 8 deletions

diff --git a/arch/ia64/kernel/entry.S b/arch/ia64/kernel/entry.S
index 6bfd8429ee0f..7a53530f22c2 100644
--- a/arch/ia64/kernel/entry.S
+++ b/arch/ia64/kernel/entry.S
@@ -724,7 +724,7 @@ GLOBAL_ENTRY(__paravirt_leave_syscall)
 #endif
 .global __paravirt_work_processed_syscall;
 __paravirt_work_processed_syscall:
-#ifdef CONFIG_VIRT_CPU_ACCOUNTING
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
         adds r2=PT(LOADRS)+16,r12
         MOV_FROM_ITC(pUStk, p9, r22, r19)       // fetch time at leave
         adds r18=TI_FLAGS+IA64_TASK_SIZE,r13
@@ -762,7 +762,7 @@ __paravirt_work_processed_syscall:
 
         ld8 r29=[r2],16         // M0|1 load cr.ipsr
         ld8 r28=[r3],16         // M0|1 load cr.iip
-#ifdef CONFIG_VIRT_CPU_ACCOUNTING
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
 (pUStk) add r14=TI_AC_LEAVE+IA64_TASK_SIZE,r13
         ;;
         ld8 r30=[r2],16         // M0|1 load cr.ifs
@@ -793,7 +793,7 @@ __paravirt_work_processed_syscall:
         ld8.fill r1=[r3],16                     // M0|1 load r1
 (pUStk) mov r17=1                               // A
         ;;
-#ifdef CONFIG_VIRT_CPU_ACCOUNTING
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
 (pUStk) st1 [r15]=r17                           // M2|3
 #else
 (pUStk) st1 [r14]=r17                           // M2|3
@@ -813,7 +813,7 @@ __paravirt_work_processed_syscall:
         shr.u r18=r19,16                // I0|1 get byte size of existing "dirty" partition
         COVER                           // B    add current frame into dirty partition & set cr.ifs
         ;;
-#ifdef CONFIG_VIRT_CPU_ACCOUNTING
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
         mov r19=ar.bsp                  // M2   get new backing store pointer
         st8 [r14]=r22                   // M    save time at leave
         mov f10=f0                      // F    clear f10
@@ -948,7 +948,7 @@ GLOBAL_ENTRY(__paravirt_leave_kernel)
         adds r16=PT(CR_IPSR)+16,r12
         adds r17=PT(CR_IIP)+16,r12
 
-#ifdef CONFIG_VIRT_CPU_ACCOUNTING
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
         .pred.rel.mutex pUStk,pKStk
         MOV_FROM_PSR(pKStk, r22, r29)   // M2 read PSR now that interrupts are disabled
         MOV_FROM_ITC(pUStk, p9, r22, r29)       // M  fetch time at leave
@@ -981,7 +981,7 @@ GLOBAL_ENTRY(__paravirt_leave_kernel)
         ;;
         ld8.fill r12=[r16],16
         ld8.fill r13=[r17],16
-#ifdef CONFIG_VIRT_CPU_ACCOUNTING
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
 (pUStk) adds r3=TI_AC_LEAVE+IA64_TASK_SIZE,r18
 #else
 (pUStk) adds r18=IA64_TASK_THREAD_ON_USTACK_OFFSET,r18
@@ -989,7 +989,7 @@ GLOBAL_ENTRY(__paravirt_leave_kernel)
         ;;
         ld8 r20=[r16],16        // ar.fpsr
         ld8.fill r15=[r17],16
-#ifdef CONFIG_VIRT_CPU_ACCOUNTING
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
 (pUStk) adds r18=IA64_TASK_THREAD_ON_USTACK_OFFSET,r18  // deferred
 #endif
         ;;
@@ -997,7 +997,7 @@ GLOBAL_ENTRY(__paravirt_leave_kernel)
         ld8.fill r2=[r17]
 (pUStk) mov r17=1
         ;;
-#ifdef CONFIG_VIRT_CPU_ACCOUNTING
+#ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
         //  mmi_ :  ld8 st1 shr;;         mmi_ : st8 st1 shr;;
         //  mib  :  mov add br        ->  mib  : ld8 add br
         //  bbb_ :  br  nop cover;;       mbb_ : mov br  cover;;