powerpc: Tell RCU about idle after hcall tracing

The PowerPC pSeries platform (CONFIG_PPC_PSERIES=y) enables
hypervisor-call tracing for CONFIG_TRACEPOINTS=y kernels.  One of the
hypervisor calls that is traced is the H_CEDE call in the idle loop
that tells the hypervisor that this OS instance no longer needs the
current CPU.  However, tracing uses RCU, so this combination of kernel
configuration variables needs to avoid telling RCU about the current CPU's
idleness until after the H_CEDE-entry tracing completes on the one hand,
and must tell RCU that the the current CPU is no longer idle before the
H_CEDE-exit tracing starts.

In all other cases, it suffices to inform RCU of CPU idleness upon
idle-loop entry and exit.

This commit makes the required adjustments.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

diff --git a/arch/powerpc/kernel/idle.c b/arch/powerpc/kernel/idle.c
index 2e782a36d8f2e321a5967e2b0e418b424a234fa9..3cd73d1fc427b3a618e26fa301e348dbcffcc064 100644 (file)
--- a/arch/powerpc/kernel/idle.c
+++ b/arch/powerpc/kernel/idle.c
@@ -46,6 +46,12 @@ static int __init powersave_off(char *arg)
 }
 __setup("powersave=off", powersave_off);
 
+#if defined(CONFIG_PPC_PSERIES) && defined(CONFIG_TRACEPOINTS)
+static const bool idle_uses_rcu = 1;
+#else
+static const bool idle_uses_rcu;
+#endif
+
 /*
  * The body of the idle task.
  */
@@ -56,7 +62,10 @@ void cpu_idle(void)
 
        set_thread_flag(TIF_POLLING_NRFLAG);
        while (1) {
-               tick_nohz_idle_enter_norcu();
+               if (idle_uses_rcu)
+                       tick_nohz_idle_enter();
+               else
+                       tick_nohz_idle_enter_norcu();
                while (!need_resched() && !cpu_should_die()) {
                        ppc64_runlatch_off();
 
@@ -93,7 +102,10 @@ void cpu_idle(void)
 
                HMT_medium();
                ppc64_runlatch_on();
-               tick_nohz_idle_exit_norcu();
+               if (idle_uses_rcu)
+                       tick_nohz_idle_exit();
+               else
+                       tick_nohz_idle_exit_norcu();
                preempt_enable_no_resched();
                if (cpu_should_die())
                        cpu_die();

diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c
index 27a49508b410711beebff40be49524c28ee3bddc..52d429be6c764a4a9e27a9efa5c1a9c5c0e819af 100644 (file)
--- a/arch/powerpc/platforms/pseries/lpar.c
+++ b/arch/powerpc/platforms/pseries/lpar.c
@@ -555,6 +555,8 @@ void __trace_hcall_entry(unsigned long opcode, unsigned long *args)
 
        (*depth)++;
        trace_hcall_entry(opcode, args);
+       if (opcode == H_CEDE)
+               rcu_idle_enter();
        (*depth)--;
 
 out:
@@ -575,6 +577,8 @@ void __trace_hcall_exit(long opcode, unsigned long retval,
                goto out;
 
        (*depth)++;
+       if (opcode == H_CEDE)
+               rcu_idle_exit();
        trace_hcall_exit(opcode, retval, retbuf);
        (*depth)--;