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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 16:00:19 -0800	[thread overview]
Message-ID: <1199923219.6350.16.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>
> ---
>  arch/x86/kernel/vsyscall_64.c |    5 ++-
>  include/asm-x86/vgtod.h       |    2 -
>  include/linux/clocksource.h   |   58 ++++++++++++++++++++++++++++++++++++++++--
>  kernel/time/timekeeping.c     |   35 +++++++++++++------------
>  4 files changed, 80 insertions(+), 20 deletions(-)
> 
> linux-2.6.21-rc5_cycles-accumulated_C7.patch
            ^^ An oldie but a goodie?

I was just reminded that in the time since 2.6.21-rc5, other arches
beside x86_64 have gained vgettimeofday implementations, and thus will
need similar update_vsyscall() tweaks as seen below to get the correct
time.

Here's the fix for x86_64:
> Index: linux-compile-i386.git/arch/x86/kernel/vsyscall_64.c
> ===================================================================
> --- linux-compile-i386.git.orig/arch/x86/kernel/vsyscall_64.c	2008-01-09 14:10:20.000000000 -0500
> +++ linux-compile-i386.git/arch/x86/kernel/vsyscall_64.c	2008-01-09 14:17:53.000000000 -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;


Tony:  ia64 also needs something like this, but I found the fsyscall asm
bits a little difficult to grasp. So I'll need some assistance on how to
include the accumulated cycles into the final calculation.


The following is a quick and dirty fix for powerpc so it includes
cycle_accumulated in its calculation. It relies on the fact that the
powerpc clocksource is a 64bit counter (don't have to worry about
multiple overflows), so the subtraction should be safe.

Signed-off-by: John Stultz <johnstul@us.ibm.com>
Index: 2.6.24-rc5/arch/powerpc/kernel/time.c
===================================================================
--- 2.6.24-rc5.orig/arch/powerpc/kernel/time.c	2008-01-09 15:17:32.000000000 -0800
+++ 2.6.24-rc5/arch/powerpc/kernel/time.c	2008-01-09 15:17:43.000000000 -0800
@@ -773,7 +773,7 @@ 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)






  reply	other threads:[~2008-01-10  0:01 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 [this message]
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   ` [RFC PATCH 13/22 -v2] handle accurate time keeping over long delays john stultz
2008-01-10  0:25     ` 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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