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From: john stultz <johnstul@us.ibm.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: LKML <linux-kernel@vger.kernel.org>, 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>,
	Steven Rostedt <srostedt@redhat.com>
Subject: Re: [RFC PATCH 13/22 -v2] handle accurate time keeping over long delays
Date: Wed, 09 Jan 2008 16:19:17 -0800	[thread overview]
Message-ID: <1199924357.6350.27.camel@localhost.localdomain> (raw)
In-Reply-To: <20080109233044.288563621@goodmis.org>


On Wed, 2008-01-09 at 18:29 -0500, Steven Rostedt wrote:
> plain text document attachment (rt-time-starvation-fix.patch)
> 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>

Hrmm.. One more item I just noticed.

> Index: linux-compile-i386.git/kernel/time/timekeeping.c
> ===================================================================
> --- linux-compile-i386.git.orig/kernel/time/timekeeping.c	2008-01-09 14:07:34.000000000 -0500
> +++ linux-compile-i386.git/kernel/time/timekeeping.c	2008-01-09 15:17:31.000000000 -0500
> @@ -448,27 +449,29 @@ static void clocksource_adjust(s64 offse
>   */
>  void update_wall_time(void)
>  {
> -	cycle_t offset;
> +	cycle_t cycle_now, offset;
> 
>  	/* 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
> +	offset = (cycle_now - clock->cycle_last) & clock->mask;

It seems this offset addition was to merge against the colliding
xtime_cache changes in mainline. However, I don't think its quite right,
and might be causing incorrect time() or vtime() results if NO_HZ is
enabled.

> +	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;
> @@ -482,7 +485,7 @@ void update_wall_time(void)
>  	}
> 
>  	/* correct the clock when NTP error is too big */
> -	clocksource_adjust(offset);
> +	clocksource_adjust(clock->cycle_accumulated);


I suspect the following is needed, but haven't been able to test it yet.

thanks
-john


Fixup merge between xtime_cache and timekeeping starvation fix.

Signed-off-by: John Stultz <johnstul@us.ibm.com>

Index: 2.6/kernel/time/timekeeping.c
===================================================================
--- 2.6.orig/kernel/time/timekeeping.c	2008-01-09 16:12:49.000000000 -0800
+++ 2.6/kernel/time/timekeeping.c	2008-01-09 16:13:18.000000000 -0800
@@ -449,7 +449,7 @@ static void clocksource_adjust(s64 offse
  */
 void update_wall_time(void)
 {
-	cycle_t cycle_now, offset;
+	cycle_t cycle_now;
 
 	/* Make sure we're fully resumed: */
 	if (unlikely(timekeeping_suspended))
@@ -460,7 +460,6 @@ void update_wall_time(void)
 #else
 	cycle_now = clock->cycle_last + clock->cycle_interval;
 #endif
-	offset = (cycle_now - clock->cycle_last) & clock->mask;
 	clocksource_accumulate(clock, cycle_now);
 
 	clock->xtime_nsec += (s64)xtime.tv_nsec << clock->shift;
@@ -491,7 +490,7 @@ void update_wall_time(void)
 	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();



  parent reply	other threads:[~2008-01-10  0:20 UTC|newest]

Thread overview: 100+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-01-09 23:29 [RFC PATCH 00/22 -v2] mcount and latency tracing utility -v2 Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 01/22 -v2] Add basic support for gcc profiler instrumentation Steven Rostedt
2008-01-10 18:19   ` Jan Kiszka
2008-01-10 19:54     ` Steven Rostedt
2008-01-10 23:02     ` Steven Rostedt
2008-01-10 18:28   ` Sam Ravnborg
2008-01-10 19:10     ` Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 02/22 -v2] Annotate core code that should not be traced Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 03/22 -v2] x86_64: notrace annotations Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 04/22 -v2] add notrace annotations to vsyscall Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 05/22 -v2] add notrace annotations for NMI routines Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 06/22 -v2] mcount based trace in the form of a header file library Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 07/22 -v2] tracer add debugfs interface Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 08/22 -v2] mcount tracer output file Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 09/22 -v2] mcount tracer show task comm and pid Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 10/22 -v2] Add a symbol only trace output Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 11/22 -v2] Reset the tracer when started Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 12/22 -v2] separate out the percpu date into a percpu struct Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 13/22 -v2] handle accurate time keeping over long delays Steven Rostedt
2008-01-10  0:00   ` john stultz
2008-01-10  0:09     ` Steven Rostedt
2008-01-10 19:54     ` Tony Luck
2008-01-10 20:15       ` Steven Rostedt
2008-01-10 20:41         ` john stultz
2008-01-10 20:29       ` john stultz
2008-01-10 20:42         ` Mathieu Desnoyers
2008-01-10 21:25           ` john stultz
2008-01-10 22:00             ` Mathieu Desnoyers
2008-01-10 22:40               ` Steven Rostedt
2008-01-10 22:51               ` john stultz
2008-01-10 23:05                 ` john stultz
2008-01-10 21:33         ` [RFC PATCH 13/22 -v2] handle accurate time keeping over longdelays Luck, Tony
2008-01-10  0:19   ` john stultz [this message]
2008-01-10  0:25     ` [RFC PATCH 13/22 -v2] handle accurate time keeping over long delays Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 14/22 -v2] time keeping add cycle_raw for actual incrementation Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 15/22 -v2] initialize the clock source to jiffies clock Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 16/22 -v2] add get_monotonic_cycles Steven Rostedt
2008-01-10  3:28   ` Daniel Walker
2008-01-15 21:46   ` Mathieu Desnoyers
2008-01-15 22:01     ` Steven Rostedt
2008-01-15 22:03       ` Steven Rostedt
2008-01-15 22:08       ` Mathieu Desnoyers
2008-01-16  1:38         ` Steven Rostedt
2008-01-16  3:17           ` Mathieu Desnoyers
2008-01-16 13:17             ` Steven Rostedt
2008-01-16 14:56               ` Mathieu Desnoyers
2008-01-16 15:06                 ` Steven Rostedt
2008-01-16 15:28                   ` Mathieu Desnoyers
2008-01-16 15:58                     ` Steven Rostedt
2008-01-16 17:00                       ` Mathieu Desnoyers
2008-01-16 17:49                         ` Mathieu Desnoyers
2008-01-16 19:43                         ` Steven Rostedt
2008-01-16 20:17                           ` Mathieu Desnoyers
2008-01-16 20:45                             ` Tim Bird
2008-01-16 20:49                             ` Steven Rostedt
2008-01-17 20:08                             ` Steven Rostedt
2008-01-17 20:37                               ` Frank Ch. Eigler
2008-01-17 21:03                                 ` Steven Rostedt
2008-01-18 22:26                                   ` Mathieu Desnoyers
2008-01-18 22:49                                     ` Steven Rostedt
2008-01-18 23:19                                       ` Mathieu Desnoyers
2008-01-19  3:36                                         ` Frank Ch. Eigler
2008-01-19  3:55                                           ` Steven Rostedt
2008-01-19  4:23                                             ` Frank Ch. Eigler
2008-01-19 15:29                                               ` Mathieu Desnoyers
2008-01-19  3:32                                       ` Frank Ch. Eigler
2008-01-16 18:01                       ` Tim Bird
2008-01-16 22:36                 ` john stultz
2008-01-16 22:51                   ` john stultz
2008-01-16 23:33                     ` Steven Rostedt
2008-01-17  2:28                       ` john stultz
2008-01-17  2:40                         ` Mathieu Desnoyers
2008-01-17  2:50                           ` Mathieu Desnoyers
2008-01-17  3:02                             ` Steven Rostedt
2008-01-17  3:21                             ` Paul Mackerras
2008-01-17  3:39                               ` Steven Rostedt
2008-01-17  4:22                                 ` Mathieu Desnoyers
2008-01-17  4:25                                 ` Mathieu Desnoyers
2008-01-17  4:14                               ` Mathieu Desnoyers
2008-01-17 15:22                                 ` Steven Rostedt
2008-01-17 17:46                                 ` Linus Torvalds
2008-01-17  2:51                           ` Steven Rostedt
2008-01-16 23:39                     ` Mathieu Desnoyers
2008-01-16 23:50                       ` Steven Rostedt
2008-01-17  0:36                         ` Steven Rostedt
2008-01-17  0:33                       ` john stultz
2008-01-17  2:20                         ` Mathieu Desnoyers
2008-01-17  1:03                       ` Linus Torvalds
2008-01-17  1:35                         ` Mathieu Desnoyers
2008-01-17  2:20                       ` john stultz
2008-01-17  2:35                         ` Mathieu Desnoyers
2008-01-09 23:29 ` [RFC PATCH 17/22 -v2] Add timestamps to tracer Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 18/22 -v2] Sort trace by timestamp Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 19/22 -v2] speed up the output of the tracer Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 20/22 -v2] Add latency_trace format tor tracer Steven Rostedt
2008-01-10  3:41   ` Daniel Walker
2008-01-09 23:29 ` [RFC PATCH 21/22 -v2] Split out specific tracing functions Steven Rostedt
2008-01-09 23:29 ` [RFC PATCH 22/22 -v2] Trace irq disabled critical timings Steven Rostedt
2008-01-10  3:58   ` Daniel Walker
2008-01-10 14:45     ` Steven Rostedt

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