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From:   "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
To:     Nicholas Piggin <npiggin@gmail.com>,
        Anton Blanchard <anton@ozlabs.org>,
        Nathan Lynch <nathanl@linux.ibm.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Michael Neuling <mikey@neuling.org>,
        Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Cc:     linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org,
        linux-pm@vger.kernel.org,
        "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>
Subject: [PATCH 1/5] cpuidle-pseries: Set the latency-hint before entering CEDE
Date:   Tue,  7 Jul 2020 16:41:35 +0530
Message-Id: <1594120299-31389-2-git-send-email-ego@linux.vnet.ibm.com>
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From: "Gautham R. Shenoy" <ego@linux.vnet.ibm.com>

As per the PAPR, each H_CEDE call is associated with a latency-hint to
be passed in the VPA field "cede_latency_hint". The CEDE states that
we were implicitly entering so far is CEDE with latency-hint = 0.

This patch explicitly sets the latency hint corresponding to the CEDE
state that we are currently entering. While at it, we save the
previous hint, to be restored once we wakeup from CEDE. This will be
required in the future when we expose extended-cede states through the
cpuidle framework, where each of them will have a different
cede-latency hint.

Signed-off-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
---
 drivers/cpuidle/cpuidle-pseries.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/drivers/cpuidle/cpuidle-pseries.c b/drivers/cpuidle/cpuidle-pseries.c
index 4a37252..39d4bb6 100644
--- a/drivers/cpuidle/cpuidle-pseries.c
+++ b/drivers/cpuidle/cpuidle-pseries.c
@@ -105,19 +105,27 @@ static void check_and_cede_processor(void)
 	}
 }
 
+#define NR_CEDE_STATES		1  /* CEDE with latency-hint 0 */
+#define NR_DEDICATED_STATES	(NR_CEDE_STATES + 1) /* Includes snooze */
+
+u8 cede_latency_hint[NR_DEDICATED_STATES];
 static int dedicated_cede_loop(struct cpuidle_device *dev,
 				struct cpuidle_driver *drv,
 				int index)
 {
+	u8 old_latency_hint;
 
 	pseries_idle_prolog();
 	get_lppaca()->donate_dedicated_cpu = 1;
+	old_latency_hint = get_lppaca()->cede_latency_hint;
+	get_lppaca()->cede_latency_hint = cede_latency_hint[index];
 
 	HMT_medium();
 	check_and_cede_processor();
 
 	local_irq_disable();
 	get_lppaca()->donate_dedicated_cpu = 0;
+	get_lppaca()->cede_latency_hint = old_latency_hint;
 
 	pseries_idle_epilog();
 
@@ -149,7 +157,7 @@ static int shared_cede_loop(struct cpuidle_device *dev,
 /*
  * States for dedicated partition case.
  */
-static struct cpuidle_state dedicated_states[] = {
+static struct cpuidle_state dedicated_states[NR_DEDICATED_STATES] = {
 	{ /* Snooze */
 		.name = "snooze",
 		.desc = "snooze",
-- 
1.9.4