Subject: [PATCH 3/3] powerpc/64s/idle: POWER9 ESL=0 stop avoid save/restore overhead

From: Nicholas Piggin <[email-masked]>
Date: Sat, 18 Nov 2017 00:08:07 +1000

When stop is executed with EC=ESL=0, it appears to execute like a
normal instruction (resuming from NIP when woken by interrupt). So all
the save/restore handling can be avoided completely. In particular NV
GPRs do not have to be saved, and MSR does not have to be switched
back to kernel MSR.

So move the test for EC=ESL=0 sleep states out to power9_idle_stop,
and return directly to the caller after stop in that case. The mtspr
to PSSCR is moved to the top of power9_offline_stop just so it matches
power9_idle_stop.

This improves performance for ping-pong benchmark with the stop0_lite
idle state by 2.54% for 2 threads in the same core, and 2.57% for
different cores.

Signed-off-by: Nicholas Piggin <[email-masked]>
---
 arch/powerpc/kernel/idle_book3s.S     | 43 +++++++++++------------------------
 arch/powerpc/platforms/powernv/idle.c |  7 +++++-
 2 files changed, 19 insertions(+), 31 deletions(-)

diff --git a/arch/powerpc/kernel/idle_book3s.S b/arch/powerpc/kernel/idle_book3s.S
index 07a306173c5a..6243da99b26c 100644
--- a/arch/powerpc/kernel/idle_book3s.S
+++ b/arch/powerpc/kernel/idle_book3s.S
@@ -324,31 +324,8 @@ enter_winkle:
 /*
  * r3 - PSSCR value corresponding to the requested stop state.
  */
-power_enter_stop:
-/*
- * Check if we are executing the lite variant with ESL=EC=0
- */
-	andis.   r4,r3,PSSCR_EC_ESL_MASK_SHIFTED
+power_enter_stop_esl:
 	clrldi   r3,r3,60 /* r3 = Bits[60:63] = Requested Level (RL) */
-	bne	 .Lhandle_esl_ec_set
-	PPC_STOP
-	li	r3,0  /* Since we didn't lose state, return 0 */
-
-	/*
-	 * pnv_wakeup_noloss() expects r12 to contain the SRR1 value so
-	 * it can determine if the wakeup reason is an HMI in
-	 * CHECK_HMI_INTERRUPT.
-	 *
-	 * However, when we wakeup with ESL=0, SRR1 will not contain the wakeup
-	 * reason, so there is no point setting r12 to SRR1.
-	 *
-	 * Further, we clear r12 here, so that we don't accidentally enter the
-	 * HMI in pnv_wakeup_noloss() if the value of r12[42:45] == WAKE_HMI.
-	 */
-	li	r12, 0
-	b 	pnv_wakeup_noloss
-
-.Lhandle_esl_ec_set:
 BEGIN_FTR_SECTION
 	/*
 	 * POWER9 DD2.0 or earlier can incorrectly set PMAO when waking up after
@@ -423,26 +400,32 @@ ALT_FTR_SECTION_END_NESTED_IFSET(CPU_FTR_ARCH_207S, 66);		\
  * r3 contains desired PSSCR register value.
  */
 _GLOBAL(power9_idle_stop)
-	std	r3, PACA_REQ_PSSCR(r13)
 	mtspr 	SPRN_PSSCR,r3
-	LOAD_REG_ADDR(r4,power_enter_stop)
+	andis.	r4,r3,PSSCR_EC_ESL_MASK_SHIFTED
+	bne	1f
+	PPC_STOP
+	li	r3,0  /* Since we didn't lose state, return 0 */
+	blr
+
+1:	std	r3, PACA_REQ_PSSCR(r13)
+	LOAD_REG_ADDR(r4,power_enter_stop_esl)
 	b	pnv_powersave_common
 	/* No return */
 
 /*
- * Entered with MSR[EE]=0 and no soft-masked interrupts pending.
- * r3 contains desired PSSCR register value.
+ * This is the same as the above, but it sets KVM state for secondaries,
+ * and it must have PSSCR[EC]=1
  */
 _GLOBAL(power9_offline_stop)
-	std	r3, PACA_REQ_PSSCR(r13)
 	mtspr 	SPRN_PSSCR,r3
+	std	r3, PACA_REQ_PSSCR(r13)
 #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
 	/* Tell KVM we're entering idle */
 	li	r4,KVM_HWTHREAD_IN_IDLE
 	/* DO THIS IN REAL MODE!  See comment above. */
 	stb	r4,HSTATE_HWTHREAD_STATE(r13)
 #endif
-	LOAD_REG_ADDR(r4,power_enter_stop)
+	LOAD_REG_ADDR(r4,power_enter_stop_esl)
 	b	pnv_powersave_common
 	/* No return */
 
diff --git a/arch/powerpc/platforms/powernv/idle.c b/arch/powerpc/platforms/powernv/idle.c
index a921d5428d76..610b1637c16f 100644
--- a/arch/powerpc/platforms/powernv/idle.c
+++ b/arch/powerpc/platforms/powernv/idle.c
@@ -621,7 +621,12 @@ static int __init pnv_power9_idle_init(struct device_node *np, u32 *flags,
 			continue;
 		}
 
-		if (max_residency_ns < residency_ns[i]) {
+		/*
+		 * Deepest stop for unplug must be PSSCR[EC]=1 (wakeup at
+		 * 0x100.
+		 */
+		if ((max_residency_ns < residency_ns[i])&&
+				(psscr_val[i] & PSSCR_EC)) {
 			max_residency_ns = residency_ns[i];
 			pnv_deepest_stop_psscr_val = psscr_val[i];
 			pnv_deepest_stop_psscr_mask = psscr_mask[i];
-- 
2.15.0