summaryrefslogtreecommitdiff
path: root/arch/powerpc/kernel/time.c
diff options
context:
space:
mode:
Diffstat (limited to 'arch/powerpc/kernel/time.c')
-rw-r--r--arch/powerpc/kernel/time.c32
1 files changed, 32 insertions, 0 deletions
diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index fa7c4f12104f..7316dd15278a 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -621,6 +621,38 @@ unsigned long long sched_clock(void)
return mulhdu(get_tb() - boot_tb, tb_to_ns_scale) << tb_to_ns_shift;
}
+
+#ifdef CONFIG_PPC_PSERIES
+
+/*
+ * Running clock - attempts to give a view of time passing for a virtualised
+ * kernels.
+ * Uses the VTB register if available otherwise a next best guess.
+ */
+unsigned long long running_clock(void)
+{
+ /*
+ * Don't read the VTB as a host since KVM does not switch in host
+ * timebase into the VTB when it takes a guest off the CPU, reading the
+ * VTB would result in reading 'last switched out' guest VTB.
+ *
+ * Host kernels are often compiled with CONFIG_PPC_PSERIES checked, it
+ * would be unsafe to rely only on the #ifdef above.
+ */
+ if (firmware_has_feature(FW_FEATURE_LPAR) &&
+ cpu_has_feature(CPU_FTR_ARCH_207S))
+ return mulhdu(get_vtb() - boot_tb, tb_to_ns_scale) << tb_to_ns_shift;
+
+ /*
+ * This is a next best approximation without a VTB.
+ * On a host which is running bare metal there should never be any stolen
+ * time and on a host which doesn't do any virtualisation TB *should* equal
+ * VTB so it makes no difference anyway.
+ */
+ return local_clock() - cputime_to_nsecs(kcpustat_this_cpu->cpustat[CPUTIME_STEAL]);
+}
+#endif
+
static int __init get_freq(char *name, int cells, unsigned long *val)
{
struct device_node *cpu;