linux-kernel - [PATCH 3/3] clocksource: mips-gic-timer: Add fastpath for local timer updates

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Date:   Wed, 11 Oct 2017 15:01:14 +0100
From:   Matt Redfearn <matt.redfearn@...s.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Daniel Lezcano <daniel.lezcano@...aro.org>
CC:     <linux-mips@...ux-mips.org>,
        Matt Redfearn <matt.redfearn@...s.com>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH 3/3] clocksource: mips-gic-timer: Add fastpath for local timer updates

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>
---

 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 dadac9f3e9c4..ca334431b0bc 100644
--- a/drivers/clocksource/mips-gic-timer.c
+++ b/drivers/clocksource/mips-gic-timer.c
@@ -39,6 +39,7 @@ 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);
 	unsigned long flags;
 	u64 cnt;
 	int res;
@@ -46,8 +47,12 @@ static int gic_next_event(unsigned long delta, struct clock_event_device *evt)
 	local_irq_save(flags);
 	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);
+	}
 	local_irq_restore(flags);
 	res = ((int)(gic_read_count() - cnt) >= 0) ? -ETIME : 0;
 	return res;
-- 
2.7.4