Subject: Re: [v3 PATCH 2/4] powernv:smp: Add busy-wait loop as fall back for CPU-Hotplug

From: Gautham R Shenoy <[email-masked]>
Date: Thu, 30 Mar 2017 14:49:15 +0530

On Mon, Mar 27, 2017 at 10:43:44PM +1100, Michael Ellerman wrote:
> "Gautham R. Shenoy" <[email-masked]> writes:
> 
> > diff --git a/arch/powerpc/platforms/powernv/idle.c b/arch/powerpc/platforms/powernv/idle.c
> > index 419edff..f335e0f 100644
> > --- a/arch/powerpc/platforms/powernv/idle.c
> > +++ b/arch/powerpc/platforms/powernv/idle.c
> > @@ -283,8 +283,16 @@ unsigned long pnv_cpu_offline(unsigned int cpu)
> >  	} else if ((idle_states & OPAL_PM_SLEEP_ENABLED) ||
> >  		   (idle_states & OPAL_PM_SLEEP_ENABLED_ER1)) {
> >  		srr1 = power7_sleep();
> > -	} else {
> > +	} else if (idle_states & OPAL_PM_NAP_ENABLED) {
> >  		srr1 = power7_nap(1);
> > +	} else {
> > +		/* This is the fallback method. We emulate snooze */
> > +		while (!generic_check_cpu_restart(cpu)) {
> 
> Breaks the SMP=n build :/

Hmmm.. Looks like I have missed adding a CONFIG_HOTPLUG_CPU somewhere.
> 
> arch/powerpc/platforms/powernv/idle.c:299:11: error: implicit declaration of function 'generic_check_cpu_restart' [-Werror=implicit-function-declaration]
>

Could you add the following patch as the PATCH 1 in the series instead
of what was present in this series ? It adds a CONFIG_HOTPLUG_CPU
around pnv_cpu_offline(). I have compiled it with both all
combinations of CONFIG_HOTPLUG_CPU and CONFIG_SMP and it builds fine.

----------------------------x-----x-----x-------------------------------
powernv: Move CPU-Offline idle state invocation from smp.c to idle.c

Move the piece of code in powernv/smp.c::pnv_smp_cpu_kill_self() which
transitions the CPU to the deepest available platform idle state to a
new function named pnv_cpu_offline() in powernv/idle.c. The rationale
behind this code movement is that the data required to determine the
deepest available platform state resides in powernv/idle.c.

Reviewed-by: Nicholas Piggin <[email-masked]>
Signed-off-by: Gautham R. Shenoy <[email-masked]>
---
Restricts pnv_cpu_offline() to CONFIG_HOTPLUG_CPU

 arch/powerpc/include/asm/cpuidle.h       |  1 +
 arch/powerpc/platforms/powernv/idle.c    | 27 +++++++++++++++++++++++++++
 arch/powerpc/platforms/powernv/powernv.h |  2 --
 arch/powerpc/platforms/powernv/smp.c     | 18 ++----------------
 4 files changed, 30 insertions(+), 18 deletions(-)

diff --git a/arch/powerpc/include/asm/cpuidle.h b/arch/powerpc/include/asm/cpuidle.h
index 1557315..4649ca0 100644
--- a/arch/powerpc/include/asm/cpuidle.h
+++ b/arch/powerpc/include/asm/cpuidle.h
@@ -46,6 +46,7 @@
 
 extern u64 pnv_first_deep_stop_state;
 
+unsigned long pnv_cpu_offline(unsigned int cpu);
 int validate_psscr_val_mask(u64 *psscr_val, u64 *psscr_mask, u32 flags);
 static inline void report_invalid_psscr_val(u64 psscr_val, int err)
 {
diff --git a/arch/powerpc/platforms/powernv/idle.c b/arch/powerpc/platforms/powernv/idle.c
index 4ee837e..fafafa3 100644
--- a/arch/powerpc/platforms/powernv/idle.c
+++ b/arch/powerpc/platforms/powernv/idle.c
@@ -265,6 +265,33 @@ static void power9_idle(void)
 u64 pnv_deepest_stop_psscr_val;
 u64 pnv_deepest_stop_psscr_mask;
 
+#ifdef CONFIG_HOTPLUG_CPU
+/*
+ * pnv_cpu_offline: A function that puts the CPU into the deepest
+ * available platform idle state on a CPU-Offline.
+ */
+unsigned long pnv_cpu_offline(unsigned int cpu)
+{
+	unsigned long srr1;
+
+	u32 idle_states = pnv_get_supported_cpuidle_states();
+
+	if (cpu_has_feature(CPU_FTR_ARCH_300)) {
+		srr1 = power9_idle_stop(pnv_deepest_stop_psscr_val,
+					pnv_deepest_stop_psscr_mask);
+	} else if (idle_states & OPAL_PM_WINKLE_ENABLED) {
+		srr1 = power7_winkle();
+	} else if ((idle_states & OPAL_PM_SLEEP_ENABLED) ||
+		   (idle_states & OPAL_PM_SLEEP_ENABLED_ER1)) {
+		srr1 = power7_sleep();
+	} else {
+		srr1 = power7_nap(1);
+	}
+
+	return srr1;
+}
+#endif
+
 /*
  * Power ISA 3.0 idle initialization.
  *
diff --git a/arch/powerpc/platforms/powernv/powernv.h b/arch/powerpc/platforms/powernv/powernv.h
index 6130522..6dbc0a1 100644
--- a/arch/powerpc/platforms/powernv/powernv.h
+++ b/arch/powerpc/platforms/powernv/powernv.h
@@ -18,8 +18,6 @@ static inline void pnv_pci_shutdown(void) { }
 #endif
 
 extern u32 pnv_get_supported_cpuidle_states(void);
-extern u64 pnv_deepest_stop_psscr_val;
-extern u64 pnv_deepest_stop_psscr_mask;
 
 extern void pnv_lpc_init(void);
 
diff --git a/arch/powerpc/platforms/powernv/smp.c b/arch/powerpc/platforms/powernv/smp.c
index 8b67e1e..914b456 100644
--- a/arch/powerpc/platforms/powernv/smp.c
+++ b/arch/powerpc/platforms/powernv/smp.c
@@ -35,6 +35,7 @@
 #include <asm/dbell.h>
 #include <asm/kvm_ppc.h>
 #include <asm/ppc-opcode.h>
+#include <asm/cpuidle.h>
 
 #include "powernv.h"
 
@@ -140,7 +141,6 @@ static void pnv_smp_cpu_kill_self(void)
 {
 	unsigned int cpu;
 	unsigned long srr1, wmask;
-	u32 idle_states;
 
 	/* Standard hot unplug procedure */
 	local_irq_disable();
@@ -155,8 +155,6 @@ static void pnv_smp_cpu_kill_self(void)
 	if (cpu_has_feature(CPU_FTR_ARCH_207S))
 		wmask = SRR1_WAKEMASK_P8;
 
-	idle_states = pnv_get_supported_cpuidle_states();
-
 	/* We don't want to take decrementer interrupts while we are offline,
 	 * so clear LPCR:PECE1. We keep PECE2 (and LPCR_PECE_HVEE on P9)
 	 * enabled as to let IPIs in.
@@ -184,19 +182,7 @@ static void pnv_smp_cpu_kill_self(void)
 		kvmppc_set_host_ipi(cpu, 0);
 
 		ppc64_runlatch_off();
-
-		if (cpu_has_feature(CPU_FTR_ARCH_300)) {
-			srr1 = power9_idle_stop(pnv_deepest_stop_psscr_val,
-						pnv_deepest_stop_psscr_mask);
-		} else if (idle_states & OPAL_PM_WINKLE_ENABLED) {
-			srr1 = power7_winkle();
-		} else if ((idle_states & OPAL_PM_SLEEP_ENABLED) ||
-			   (idle_states & OPAL_PM_SLEEP_ENABLED_ER1)) {
-			srr1 = power7_sleep();
-		} else {
-			srr1 = power7_nap(1);
-		}
-
+		srr1 = pnv_cpu_offline(cpu);
 		ppc64_runlatch_on();
 
 		/*
-- 
1.9.4