powerpc/64: remove start_tb and accum_tb from thread_struct

These fields are only written to.
Signed-off-by: NNicholas Piggin <npiggin@gmail.com>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/processor.h

@@ -264,10 +264,6 @@ struct thread_struct {
 	struct thread_fp_state	*fp_save_area;
 	int		fpexc_mode;	/* floating-point exception mode */
 	unsigned int	align_ctl;	/* alignment handling control */
-#ifdef CONFIG_PPC64
-	unsigned long	start_tb;	/* Start purr when proc switched in */
-	unsigned long	accum_tb;	/* Total accumulated purr for process */
-#endif
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
 	struct perf_event *ptrace_bps[HBP_NUM];
 	/*

arch/powerpc/kernel/process.c

@@ -1188,11 +1188,7 @@ struct task_struct *__switch_to(struct task_struct *prev,
 	 */
 	if (firmware_has_feature(FW_FEATURE_SPLPAR)) {
 		struct cpu_usage *cu = this_cpu_ptr(&cpu_usage_array);
-		long unsigned start_tb, current_tb;
-		start_tb = old_thread->start_tb;
-		cu->current_tb = current_tb = mfspr(SPRN_PURR);
-		old_thread->accum_tb += (current_tb - start_tb);
-		new_thread->start_tb = current_tb;
+		cu->current_tb = mfspr(SPRN_PURR);
 	}
 #endif /* CONFIG_PPC64 */