linux-kernel - [PATCH 1/3] hrtimer: Add support for CLOCK_MONOTONIC

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Date:	Fri, 15 Jan 2016 17:41:08 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	<linux-kernel@...r.kernel.org>, Tomasz Nowicki <tn@...ihalf.com>,
	Christoffer Dall <christoffer.dall@...aro.org>
Subject: [PATCH 1/3] hrtimer: Add support for CLOCK_MONOTONIC_RAW

The KVM/ARM timer implementation arms a hrtimer when a vcpu is
blocked (usually because it is waiting for an interrupt)
while its timer is going to kick in the future.

It is essential that this timer doesn't get adjusted, or the
guest will end up being woken-up at the wrong time (NTP running
on the host seems to confuse the hell out of some guests).

In order to allow this, let's add CLOCK_MONOTONIC_RAW support
to hrtimer (it is so far only supported for posix timers). It also
has the (limited) benefit of fixing de0421d53bfb ("mac80211_hwsim:
shuffle code to prepare for dynamic radios"), which already uses
this functionnality without realizing wasn't implemented (just being
lucky...).

Signed-off-by: Marc Zyngier <marc.zyngier@....com>
---
 include/linux/hrtimer.h |  1 +
 kernel/time/hrtimer.c   | 11 ++++++++++-
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/include/linux/hrtimer.h b/include/linux/hrtimer.h
index 76dd4f0..a6d64af 100644
--- a/include/linux/hrtimer.h
+++ b/include/linux/hrtimer.h
@@ -151,6 +151,7 @@ enum  hrtimer_base_type {
 	HRTIMER_BASE_REALTIME,
 	HRTIMER_BASE_BOOTTIME,
 	HRTIMER_BASE_TAI,
+	HRTIMER_BASE_MONOTONIC_RAW,
 	HRTIMER_MAX_CLOCK_BASES,
 };
 
diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index 435b885..a125f22 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -90,12 +90,18 @@ DEFINE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases) =
 			.clockid = CLOCK_TAI,
 			.get_time = &ktime_get_clocktai,
 		},
+		{
+			.index = HRTIMER_BASE_MONOTONIC_RAW,
+			.clockid = CLOCK_MONOTONIC_RAW,
+			.get_time = &ktime_get_raw,
+		},
 	}
 };
 
 static const int hrtimer_clock_to_base_table[MAX_CLOCKS] = {
 	[CLOCK_REALTIME]	= HRTIMER_BASE_REALTIME,
 	[CLOCK_MONOTONIC]	= HRTIMER_BASE_MONOTONIC,
+	[CLOCK_MONOTONIC_RAW]	= HRTIMER_BASE_MONOTONIC_RAW,
 	[CLOCK_BOOTTIME]	= HRTIMER_BASE_BOOTTIME,
 	[CLOCK_TAI]		= HRTIMER_BASE_TAI,
 };
@@ -1268,7 +1274,10 @@ static void __hrtimer_run_queues(struct hrtimer_cpu_base *cpu_base, ktime_t now)
 		if (!(active & 0x01))
 			continue;
 
-		basenow = ktime_add(now, base->offset);
+		if (unlikely(base->index == HRTIMER_BASE_MONOTONIC_RAW))
+			basenow = ktime_get_raw();
+		else
+			basenow = ktime_add(now, base->offset);
 
 		while ((node = timerqueue_getnext(&base->active))) {
 			struct hrtimer *timer;
-- 
2.1.4