linux-kernel - [PATCH 16/17] clocksource/drivers/mips-gic-timer: Add fastpath for local timer updates

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Date:   Sun, 29 Oct 2017 22:20:33 +0100
From:   Daniel Lezcano <daniel.lezcano@...aro.org>
To:     tglx@...utronix.de, daniel.lezcano@...aro.org
Cc:     linux-kernel@...r.kernel.org,
        Matt Redfearn <matt.redfearn@...s.com>
Subject: [PATCH 16/17] clocksource/drivers/mips-gic-timer: Add fastpath for local timer updates

From: Matt Redfearn <matt.redfearn@...s.com>

Always accessing the compare register via the CM redirect region is
(relatively) slow. If the timer being updated is the current CPUs
then this can be shortcutted by writing to the CM VP local region.

Signed-off-by: Matt Redfearn <matt.redfearn@...s.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@...aro.org>
---
 drivers/clocksource/mips-gic-timer.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/clocksource/mips-gic-timer.c b/drivers/clocksource/mips-gic-timer.c
index 775dea0..a04808a 100644
--- a/drivers/clocksource/mips-gic-timer.c
+++ b/drivers/clocksource/mips-gic-timer.c
@@ -39,13 +39,18 @@ static u64 notrace gic_read_count(void)
 
 static int gic_next_event(unsigned long delta, struct clock_event_device *evt)
 {
+	int cpu = cpumask_first(evt->cpumask);
 	u64 cnt;
 	int res;
 
 	cnt = gic_read_count();
 	cnt += (u64)delta;
-	write_gic_vl_other(mips_cm_vp_id(cpumask_first(evt->cpumask)));
-	write_gic_vo_compare(cnt);
+	if (cpu == raw_smp_processor_id()) {
+		write_gic_vl_compare(cnt);
+	} else {
+		write_gic_vl_other(mips_cm_vp_id(cpu));
+		write_gic_vo_compare(cnt);
+	}
 	res = ((int)(gic_read_count() - cnt) >= 0) ? -ETIME : 0;
 	return res;
 }
-- 
2.7.4