linux-kernel - [KVM timekeeping] Revert getnsboottime() kernel API

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Message-Id: <1283320624-31262-1-git-send-email-zamsden@redhat.com>
Date:	Tue, 31 Aug 2010 19:57:04 -1000
From:	Zachary Amsden <zamsden@...hat.com>
To:	kvm@...r.kernel.org
Cc:	Zachary Amsden <zamsden@...hat.com>, Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Glauber Costa <glommer@...hat.com>,
	Jan Kiszka <jan.kiszka@....de>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <johnstul@...ibm.com>, linux-kernel@...r.kernel.org
Subject: [KVM timekeeping] Revert getnsboottime() kernel API

Turns out this doesn't actually save any math or locking, name
is chosen rather poorly, it doesn't match the existing kernel
APIs, and requires kvm-kmod changes.

Signed-off-by: Zachary Amsden <zamsden@...hat.com>
---
 arch/x86/kvm/x86.c        |   18 ++++++++++++++----
 include/linux/time.h      |    1 -
 kernel/time/timekeeping.c |   28 +---------------------------
 3 files changed, 15 insertions(+), 32 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4014d6c..03605b8 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -919,6 +919,16 @@ static inline u64 nsec_to_cycles(u64 nsec)
 	return ret;
 }
 
+static inline u64 get_kernel_ns(void)
+{
+	struct timespec ts;
+
+	WARN_ON(preemptible());
+	ktime_get_ts(&ts);
+	monotonic_to_bootbased(&ts);
+	return timespec_to_ns(&ts);
+}
+
 void kvm_write_tsc(struct kvm_vcpu *vcpu, u64 data)
 {
 	struct kvm *kvm = vcpu->kvm;
@@ -928,7 +938,7 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, u64 data)
 
 	spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags);
 	offset = data - native_read_tsc();
-	ns = getnsboottime();
+	ns = get_kernel_ns();
 	elapsed = ns - kvm->arch.last_tsc_nsec;
 	sdiff = data - kvm->arch.last_tsc_write;
 	if (sdiff < 0)
@@ -981,7 +991,7 @@ static int kvm_write_guest_time(struct kvm_vcpu *v)
 	/* Keep irq disabled to prevent changes to the clock */
 	local_irq_save(flags);
 	kvm_get_msr(v, MSR_IA32_TSC, &tsc_timestamp);
-	kernel_ns = getnsboottime();
+	kernel_ns = get_kernel_ns();
 	this_tsc_khz = __get_cpu_var(cpu_tsc_khz);
 	local_irq_restore(flags);
 
@@ -3327,7 +3337,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
 			goto out;
 
 		r = 0;
-		now_ns = getnsboottime();
+		now_ns = get_kernel_ns();
 		delta = user_ns.clock - now_ns;
 		kvm->arch.kvmclock_offset = delta;
 		break;
@@ -3336,7 +3346,7 @@ long kvm_arch_vm_ioctl(struct file *filp,
 		struct kvm_clock_data user_ns;
 		u64 now_ns;
 
-		now_ns = getnsboottime();
+		now_ns = get_kernel_ns();
 		user_ns.clock = kvm->arch.kvmclock_offset + now_ns;
 		user_ns.flags = 0;
 
diff --git a/include/linux/time.h b/include/linux/time.h
index 909e62a..9f15ac7 100644
--- a/include/linux/time.h
+++ b/include/linux/time.h
@@ -160,7 +160,6 @@ extern void getnstimeofday(struct timespec *tv);
 extern void getrawmonotonic(struct timespec *ts);
 extern void getboottime(struct timespec *ts);
 extern void monotonic_to_bootbased(struct timespec *ts);
-extern s64 getnsboottime(void);
 
 extern struct timespec timespec_trunc(struct timespec t, unsigned gran);
 extern int timekeeping_valid_for_hres(void);
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 77e930d..dfbe271 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -284,33 +284,6 @@ void ktime_get_ts(struct timespec *ts)
 }
 EXPORT_SYMBOL_GPL(ktime_get_ts);
 
-
-/**
- * getnsboottime - get the bootbased clock in nsec format
- *
- * The function calculates the bootbased clock from the realtime
- * clock and the wall_to_monotonic offset and stores the result
- * in normalized timespec format in the variable pointed to by @ts.
- */
-s64 getnsboottime(void)
-{
-	unsigned int seq;
-	s64 secs, nsecs;
-
-	WARN_ON(timekeeping_suspended);
-
-	do {
-		seq = read_seqbegin(&xtime_lock);
-		secs = xtime.tv_sec + wall_to_monotonic.tv_sec;
-		secs += total_sleep_time.tv_sec;
-		nsecs = xtime.tv_nsec + wall_to_monotonic.tv_nsec;
-		nsecs += total_sleep_time.tv_nsec + timekeeping_get_ns();
-
-	} while (read_seqretry(&xtime_lock, seq));
-	return nsecs + (secs * NSEC_PER_SEC);
-}
-EXPORT_SYMBOL_GPL(getnsboottime);
-
 /**
  * do_gettimeofday - Returns the time of day in a timeval
  * @tv:		pointer to the timeval to be set
@@ -327,6 +300,7 @@ void do_gettimeofday(struct timeval *tv)
 }
 
 EXPORT_SYMBOL(do_gettimeofday);
+
 /**
  * do_settimeofday - Sets the time of day
  * @tv:		pointer to the timespec variable containing the new time
-- 
1.7.1

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