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From: Steven Rostedt <rostedt@goodmis.org>
To: LKML <linux-kernel@vger.kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Christoph Hellwig <hch@infradead.org>,
	Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
	Gregory Haskins <ghaskins@novell.com>,
	Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
	Thomas Gleixner <tglx@linutronix.de>,
	Tim Bird <tim.bird@am.sony.com>, Sam Ravnborg <sam@ravnborg.org>,
	"Frank Ch. Eigler" <fche@redhat.com>,
	Jan Kiszka <jan.kiszka@siemens.com>,
	John Stultz <johnstul@us.ibm.com>,
	Arjan van de Ven <arjan@infradead.org>,
	Steven Rostedt <srostedt@redhat.com>
Subject: [PATCH 06/22 -v7] handle accurate time keeping over long delays
Date: Tue, 29 Jan 2008 22:15:27 -0500	[thread overview]
Message-ID: <20080130031840.992832719@goodmis.org> (raw)
In-Reply-To: <20080130031521.258552785@goodmis.org>

[-- Attachment #1: rt-time-starvation-fix.patch --]
[-- Type: text/plain, Size: 10266 bytes --]

Handle accurate time even if there's a long delay between
accumulated clock cycles.

Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
---
 arch/powerpc/kernel/time.c    |    3 +-
 arch/x86/kernel/vsyscall_64.c |    5 ++-
 include/asm-x86/vgtod.h       |    2 -
 include/linux/clocksource.h   |   58 ++++++++++++++++++++++++++++++++++++++++--
 kernel/time/timekeeping.c     |   36 +++++++++++++-------------
 5 files changed, 82 insertions(+), 22 deletions(-)

Index: linux-mcount.git/arch/x86/kernel/vsyscall_64.c
===================================================================
--- linux-mcount.git.orig/arch/x86/kernel/vsyscall_64.c	2008-01-25 21:47:06.000000000 -0500
+++ linux-mcount.git/arch/x86/kernel/vsyscall_64.c	2008-01-25 21:47:09.000000000 -0500
@@ -86,6 +86,7 @@ void update_vsyscall(struct timespec *wa
 	vsyscall_gtod_data.clock.mask = clock->mask;
 	vsyscall_gtod_data.clock.mult = clock->mult;
 	vsyscall_gtod_data.clock.shift = clock->shift;
+	vsyscall_gtod_data.clock.cycle_accumulated = clock->cycle_accumulated;
 	vsyscall_gtod_data.wall_time_sec = wall_time->tv_sec;
 	vsyscall_gtod_data.wall_time_nsec = wall_time->tv_nsec;
 	vsyscall_gtod_data.wall_to_monotonic = wall_to_monotonic;
@@ -121,7 +122,7 @@ static __always_inline long time_syscall
 
 static __always_inline void do_vgettimeofday(struct timeval * tv)
 {
-	cycle_t now, base, mask, cycle_delta;
+	cycle_t now, base, accumulated, mask, cycle_delta;
 	unsigned seq;
 	unsigned long mult, shift, nsec;
 	cycle_t (*vread)(void);
@@ -135,6 +136,7 @@ static __always_inline void do_vgettimeo
 		}
 		now = vread();
 		base = __vsyscall_gtod_data.clock.cycle_last;
+		accumulated  = __vsyscall_gtod_data.clock.cycle_accumulated;
 		mask = __vsyscall_gtod_data.clock.mask;
 		mult = __vsyscall_gtod_data.clock.mult;
 		shift = __vsyscall_gtod_data.clock.shift;
@@ -145,6 +147,7 @@ static __always_inline void do_vgettimeo
 
 	/* calculate interval: */
 	cycle_delta = (now - base) & mask;
+	cycle_delta += accumulated;
 	/* convert to nsecs: */
 	nsec += (cycle_delta * mult) >> shift;
 
Index: linux-mcount.git/include/asm-x86/vgtod.h
===================================================================
--- linux-mcount.git.orig/include/asm-x86/vgtod.h	2008-01-25 21:46:50.000000000 -0500
+++ linux-mcount.git/include/asm-x86/vgtod.h	2008-01-25 21:47:09.000000000 -0500
@@ -15,7 +15,7 @@ struct vsyscall_gtod_data {
 	struct timezone sys_tz;
 	struct { /* extract of a clocksource struct */
 		cycle_t (*vread)(void);
-		cycle_t	cycle_last;
+		cycle_t	cycle_last, cycle_accumulated;
 		cycle_t	mask;
 		u32	mult;
 		u32	shift;
Index: linux-mcount.git/include/linux/clocksource.h
===================================================================
--- linux-mcount.git.orig/include/linux/clocksource.h	2008-01-25 21:46:50.000000000 -0500
+++ linux-mcount.git/include/linux/clocksource.h	2008-01-25 21:47:09.000000000 -0500
@@ -50,8 +50,12 @@ struct clocksource;
  * @flags:		flags describing special properties
  * @vread:		vsyscall based read
  * @resume:		resume function for the clocksource, if necessary
+ * @cycle_last:		Used internally by timekeeping core, please ignore.
+ * @cycle_accumulated:	Used internally by timekeeping core, please ignore.
  * @cycle_interval:	Used internally by timekeeping core, please ignore.
  * @xtime_interval:	Used internally by timekeeping core, please ignore.
+ * @xtime_nsec:		Used internally by timekeeping core, please ignore.
+ * @error:		Used internally by timekeeping core, please ignore.
  */
 struct clocksource {
 	/*
@@ -82,7 +86,10 @@ struct clocksource {
 	 * Keep it in a different cache line to dirty no
 	 * more than one cache line.
 	 */
-	cycle_t cycle_last ____cacheline_aligned_in_smp;
+	struct {
+		cycle_t cycle_last, cycle_accumulated;
+	} ____cacheline_aligned_in_smp;
+
 	u64 xtime_nsec;
 	s64 error;
 
@@ -168,11 +175,44 @@ static inline cycle_t clocksource_read(s
 }
 
 /**
+ * clocksource_get_cycles: - Access the clocksource's accumulated cycle value
+ * @cs:		pointer to clocksource being read
+ * @now:	current cycle value
+ *
+ * Uses the clocksource to return the current cycle_t value.
+ * NOTE!!!: This is different from clocksource_read, because it
+ * returns the accumulated cycle value! Must hold xtime lock!
+ */
+static inline cycle_t
+clocksource_get_cycles(struct clocksource *cs, cycle_t now)
+{
+	cycle_t offset = (now - cs->cycle_last) & cs->mask;
+	offset += cs->cycle_accumulated;
+	return offset;
+}
+
+/**
+ * clocksource_accumulate: - Accumulates clocksource cycles
+ * @cs:		pointer to clocksource being read
+ * @now:	current cycle value
+ *
+ * Used to avoids clocksource hardware overflow by periodically
+ * accumulating the current cycle delta. Must hold xtime write lock!
+ */
+static inline void clocksource_accumulate(struct clocksource *cs, cycle_t now)
+{
+	cycle_t offset = (now - cs->cycle_last) & cs->mask;
+	cs->cycle_last = now;
+	cs->cycle_accumulated += offset;
+}
+
+/**
  * cyc2ns - converts clocksource cycles to nanoseconds
  * @cs:		Pointer to clocksource
  * @cycles:	Cycles
  *
  * Uses the clocksource and ntp ajdustment to convert cycle_ts to nanoseconds.
+ * Must hold xtime lock!
  *
  * XXX - This could use some mult_lxl_ll() asm optimization
  */
@@ -184,13 +224,27 @@ static inline s64 cyc2ns(struct clocksou
 }
 
 /**
+ * ns2cyc - converts nanoseconds to clocksource cycles
+ * @cs:		Pointer to clocksource
+ * @nsecs:	Nanoseconds
+ */
+static inline cycle_t ns2cyc(struct clocksource *cs, u64 nsecs)
+{
+	cycle_t ret = nsecs << cs->shift;
+
+	do_div(ret, cs->mult + 1);
+
+	return ret;
+}
+
+/**
  * clocksource_calculate_interval - Calculates a clocksource interval struct
  *
  * @c:		Pointer to clocksource.
  * @length_nsec: Desired interval length in nanoseconds.
  *
  * Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
- * pair and interval request.
+ * pair and interval request. Must hold xtime_lock!
  *
  * Unless you're the timekeeping code, you should not be using this!
  */
Index: linux-mcount.git/kernel/time/timekeeping.c
===================================================================
--- linux-mcount.git.orig/kernel/time/timekeeping.c	2008-01-25 21:46:50.000000000 -0500
+++ linux-mcount.git/kernel/time/timekeeping.c	2008-01-25 21:47:09.000000000 -0500
@@ -66,16 +66,10 @@ static struct clocksource *clock; /* poi
  */
 static inline s64 __get_nsec_offset(void)
 {
-	cycle_t cycle_now, cycle_delta;
+	cycle_t cycle_delta;
 	s64 ns_offset;
 
-	/* read clocksource: */
-	cycle_now = clocksource_read(clock);
-
-	/* calculate the delta since the last update_wall_time: */
-	cycle_delta = (cycle_now - clock->cycle_last) & clock->mask;
-
-	/* convert to nanoseconds: */
+	cycle_delta = clocksource_get_cycles(clock, clocksource_read(clock));
 	ns_offset = cyc2ns(clock, cycle_delta);
 
 	return ns_offset;
@@ -195,7 +189,7 @@ static void change_clocksource(void)
 
 	clock = new;
 	clock->cycle_last = now;
-
+	clock->cycle_accumulated = 0;
 	clock->error = 0;
 	clock->xtime_nsec = 0;
 	clocksource_calculate_interval(clock, NTP_INTERVAL_LENGTH);
@@ -205,9 +199,15 @@ static void change_clocksource(void)
 	printk(KERN_INFO "Time: %s clocksource has been installed.\n",
 	       clock->name);
 }
+
+void timekeeping_accumulate(void)
+{
+	clocksource_accumulate(clock, clocksource_read(clock));
+}
 #else
 static inline void change_clocksource(void) { }
 static inline s64 __get_nsec_offset(void) { return 0; }
+void timekeeping_accumulate(void) { }
 #endif
 
 /**
@@ -302,6 +302,7 @@ static int timekeeping_resume(struct sys
 	timespec_add_ns(&xtime, timekeeping_suspend_nsecs);
 	/* re-base the last cycle value */
 	clock->cycle_last = clocksource_read(clock);
+	clock->cycle_accumulated = 0;
 	clock->error = 0;
 	timekeeping_suspended = 0;
 	write_sequnlock_irqrestore(&xtime_lock, flags);
@@ -448,27 +449,28 @@ static void clocksource_adjust(s64 offse
  */
 void update_wall_time(void)
 {
-	cycle_t offset;
+	cycle_t cycle_now;
 
 	/* Make sure we're fully resumed: */
 	if (unlikely(timekeeping_suspended))
 		return;
 
 #ifdef CONFIG_GENERIC_TIME
-	offset = (clocksource_read(clock) - clock->cycle_last) & clock->mask;
+	cycle_now = clocksource_read(clock);
 #else
-	offset = clock->cycle_interval;
+	cycle_now = clock->cycle_last + clock->cycle_interval;
 #endif
+	clocksource_accumulate(clock, cycle_now);
+
 	clock->xtime_nsec += (s64)xtime.tv_nsec << clock->shift;
 
 	/* normally this loop will run just once, however in the
 	 * case of lost or late ticks, it will accumulate correctly.
 	 */
-	while (offset >= clock->cycle_interval) {
+	while (clock->cycle_accumulated >= clock->cycle_interval) {
 		/* accumulate one interval */
 		clock->xtime_nsec += clock->xtime_interval;
-		clock->cycle_last += clock->cycle_interval;
-		offset -= clock->cycle_interval;
+		clock->cycle_accumulated -= clock->cycle_interval;
 
 		if (clock->xtime_nsec >= (u64)NSEC_PER_SEC << clock->shift) {
 			clock->xtime_nsec -= (u64)NSEC_PER_SEC << clock->shift;
@@ -482,13 +484,13 @@ void update_wall_time(void)
 	}
 
 	/* correct the clock when NTP error is too big */
-	clocksource_adjust(offset);
+	clocksource_adjust(clock->cycle_accumulated);
 
 	/* store full nanoseconds into xtime */
 	xtime.tv_nsec = (s64)clock->xtime_nsec >> clock->shift;
 	clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift;
 
-	update_xtime_cache(cyc2ns(clock, offset));
+	update_xtime_cache(cyc2ns(clock, clock->cycle_accumulated));
 
 	/* check to see if there is a new clocksource to use */
 	change_clocksource();
Index: linux-mcount.git/arch/powerpc/kernel/time.c
===================================================================
--- linux-mcount.git.orig/arch/powerpc/kernel/time.c	2008-01-25 21:46:50.000000000 -0500
+++ linux-mcount.git/arch/powerpc/kernel/time.c	2008-01-25 21:47:09.000000000 -0500
@@ -773,7 +773,8 @@ void update_vsyscall(struct timespec *wa
 	stamp_xsec = (u64) xtime.tv_nsec * XSEC_PER_SEC;
 	do_div(stamp_xsec, 1000000000);
 	stamp_xsec += (u64) xtime.tv_sec * XSEC_PER_SEC;
-	update_gtod(clock->cycle_last, stamp_xsec, t2x);
+	update_gtod(clock->cycle_last-clock->cycle_accumulated,
+		    stamp_xsec, t2x);
 }
 
 void update_vsyscall_tz(void)

-- 

  parent reply	other threads:[~2008-01-30  3:27 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-01-30  3:15 [PATCH 00/22 -v7] mcount and latency tracing utility -v7 Steven Rostedt
2008-01-30  3:15 ` [PATCH 01/22 -v7] printk - dont wakeup klogd with interrupts disabled Steven Rostedt
2008-01-30  3:15 ` [PATCH 02/22 -v7] Add basic support for gcc profiler instrumentation Steven Rostedt
2008-01-30  8:46   ` Peter Zijlstra
2008-01-30 13:08     ` Steven Rostedt
2008-01-30 14:09       ` Steven Rostedt
2008-01-30 14:25         ` Peter Zijlstra
2008-02-01 22:34           ` Paul E. McKenney
2008-02-02  1:56             ` Steven Rostedt
2008-02-02 21:41               ` Paul E. McKenney
2008-02-04 17:09                 ` Steven Rostedt
2008-02-04 21:40                   ` Paul E. McKenney
2008-02-04 22:03                     ` Steven Rostedt
2008-02-04 22:41                       ` Mathieu Desnoyers
2008-02-05  6:11                         ` Paul E. McKenney
2008-02-05  5:13                       ` Paul E. McKenney
2008-01-30 13:21   ` Jan Kiszka
2008-01-30 13:53     ` Steven Rostedt
2008-01-30 14:28       ` Steven Rostedt
2008-01-30  3:15 ` [PATCH 03/22 -v7] Annotate core code that should not be traced Steven Rostedt
2008-01-30  3:15 ` [PATCH 04/22 -v7] x86_64: notrace annotations Steven Rostedt
2008-01-30  3:15 ` [PATCH 05/22 -v7] add notrace annotations to vsyscall Steven Rostedt
2008-01-30  8:49   ` Peter Zijlstra
2008-01-30 13:15     ` Steven Rostedt
2008-01-30  3:15 ` Steven Rostedt [this message]
2008-01-30  3:15 ` [PATCH 07/22 -v7] initialize the clock source to jiffies clock Steven Rostedt
2008-01-30  3:15 ` [PATCH 08/22 -v7] add get_monotonic_cycles Steven Rostedt
2008-01-30  3:15 ` [PATCH 09/22 -v7] add notrace annotations to timing events Steven Rostedt
2008-01-30  3:15 ` [PATCH 10/22 -v7] mcount based trace in the form of a header file library Steven Rostedt
2008-01-30  3:15 ` [PATCH 11/22 -v7] Add context switch marker to sched.c Steven Rostedt
2008-01-30  3:15 ` [PATCH 12/22 -v7] Make the task State char-string visible to all Steven Rostedt
2008-01-30  3:15 ` [PATCH 13/22 -v7] Add tracing of context switches Steven Rostedt
2008-01-30  3:15 ` [PATCH 14/22 -v7] Generic command line storage Steven Rostedt
2008-01-30  3:15 ` [PATCH 15/22 -v7] trace generic call to schedule switch Steven Rostedt
2008-01-30  3:15 ` [PATCH 16/22 -v7] Add marker in try_to_wake_up Steven Rostedt
2008-01-30  3:15 ` [PATCH 17/22 -v7] mcount tracer for wakeup latency timings Steven Rostedt
2008-01-30  9:31   ` Peter Zijlstra
2008-01-30 13:18     ` Steven Rostedt
2008-01-30  3:15 ` [PATCH 18/22 -v7] Trace irq disabled critical timings Steven Rostedt
2008-01-30  3:15 ` [PATCH 19/22 -v7] trace preempt off " Steven Rostedt
2008-01-30  9:40   ` Peter Zijlstra
2008-01-30 13:40     ` Steven Rostedt
2008-01-30  3:15 ` [PATCH 20/22 -v7] Add markers to various events Steven Rostedt
2008-01-30  3:15 ` [PATCH 21/22 -v7] Add event tracer Steven Rostedt
2008-01-30  3:15 ` [PATCH 22/22 -v7] Critical latency timings histogram Steven Rostedt

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