linux-kernel - [PATCH v4 1/4] cpufreq: powernv: Remove cpu_to_chip

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Message-Id: <1452545680-11976-2-git-send-email-shilpa.bhat@linux.vnet.ibm.com>
Date:	Mon, 11 Jan 2016 14:54:37 -0600
From:	Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
To:	linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org
Cc:	rjw@...ysocki.net, viresh.kumar@...aro.org,
	linux-pm@...r.kernel.org, pc@...ibm.com, anton@...ba.org,
	ego@...ux.vnet.ibm.com, <stable@...r.kernel.org>,
	Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
Subject: [PATCH v4 1/4] cpufreq: powernv: Remove cpu_to_chip_id() from hot-path

cpu_to_chip_id() does a DT walk through to find out the chip id by taking a
contended device tree lock. This adds an unnecessary overhead in a hot-path.
So instead of cpu_to_chip_id() use PIR of the cpu to find the chip id.

Reported-by: Anton Blanchard <anton@...ba.org>
Signed-off-by: Shilpasri G Bhat <shilpa.bhat@...ux.vnet.ibm.com>
---
 drivers/cpufreq/powernv-cpufreq.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
index cb50138..597a084 100644
--- a/drivers/cpufreq/powernv-cpufreq.c
+++ b/drivers/cpufreq/powernv-cpufreq.c
@@ -39,6 +39,7 @@
 #define PMSR_PSAFE_ENABLE	(1UL << 30)
 #define PMSR_SPR_EM_DISABLE	(1UL << 31)
 #define PMSR_MAX(x)		((x >> 32) & 0xFF)
+#define pir_to_chip_id(pir)	(((pir) >> 7) & 0x3f)
 
 static struct cpufreq_frequency_table powernv_freqs[POWERNV_MAX_PSTATES+1];
 static bool rebooting, throttled, occ_reset;
@@ -312,13 +313,14 @@ static inline unsigned int get_nominal_index(void)
 static void powernv_cpufreq_throttle_check(void *data)
 {
 	unsigned int cpu = smp_processor_id();
+	unsigned int chip_id = pir_to_chip_id(hard_smp_processor_id());
 	unsigned long pmsr;
 	int pmsr_pmax, i;
 
 	pmsr = get_pmspr(SPRN_PMSR);
 
 	for (i = 0; i < nr_chips; i++)
-		if (chips[i].id == cpu_to_chip_id(cpu))
+		if (chips[i].id == chip_id)
 			break;
 
 	/* Check for Pmax Capping */
@@ -558,7 +560,8 @@ static int init_chip_info(void)
 	unsigned int prev_chip_id = UINT_MAX;
 
 	for_each_possible_cpu(cpu) {
-		unsigned int id = cpu_to_chip_id(cpu);
+		unsigned int id =
+			pir_to_chip_id(get_hard_smp_processor_id(cpu));
 
 		if (prev_chip_id != id) {
 			prev_chip_id = id;
-- 
1.9.1