[ltt-dev] (forw) [RFC patch 08/15] LTTng - Timestamping

[Masami Hiramatsu]

Hi Mathieu,

These patches seems generally good. However, I wonder why you added
"ltt_" prefix. if it was useful for other parts of the kernel
(I think so), more general name(generic_timestamp?) would be preferable :)

Thank you,

Mathieu Desnoyers wrote:
> Hello,
> 
> Too many CCs on this last post. I should probably have added some, but
> here is a link to the thread :
> 
> http://lkml.org/lkml/2008/10/16/511
> 
> Comments are welcome.
> 
> Mathieu
> 
> ----- Forwarded message from Mathieu Desnoyers <mathieu.desnoyers at polymtl.ca> -----
> 
> Date: Thu, 16 Oct 2008 19:27:37 -0400
> To: Linus Torvalds <torvalds at linux-foundation.org>,
> 	Andrew Morton <akpm at linux-foundation.org>,
> 	Ingo Molnar <mingo at elte.hu>, linux-kernel at vger.kernel.org,
> 	linux-arch at vger.kernel.org, Steven Rostedt <rostedt at goodmis.org>,
> 	Peter Zijlstra <a.p.zijlstra at chello.nl>,
> 	Thomas Gleixner <tglx at linutronix.de>
> Cc: David Miller <davem at davemloft.net>,
> 	Mathieu Desnoyers <mathieu.desnoyers at polymtl.ca>,
> 	Ralf Baechle <ralf at linux-mips.org>, benh at kernel.crashing.org,
> 	paulus at samba.org, Ingo Molnar <mingo at redhat.com>
> User-Agent: quilt/0.46-1
> From: Mathieu Desnoyers <mathieu.desnoyers at polymtl.ca>
> Subject: [RFC patch 08/15] LTTng - Timestamping
> 
> Wrapper to use the lower level clock sources available on the systems. Fall-back
> on jiffies or'd with a logical clock for architectures lacking CPU timestamp
> counters. Fall-back on a mixed TSC-logical clock on architectures lacking
> synchronized TSC on SMP.
> 
> A generic fallback based on a logical clock and the timer interrupt is
> available.
> 
> generic - Uses jiffies or'd with a logical clock extended to 64 bits by
>           ltt-timestamp.c.
> i386 - Uses TSC. If detects non synchronized TSC, uses mixed TSC-logical clock.
> mips - Uses TSC extended atomically from 32 to 64 bits by ltt-heartbeat.c.
> powerpc - Uses TSC or generic ltt clock.
> x86_64 - Uses TSC. If detects non synchronized TSC, uses mixed TSC-logical clock
> 
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at polymtl.ca>
> CC: Ralf Baechle <ralf at linux-mips.org>
> CC: benh at kernel.crashing.org
> CC: paulus at samba.org
> CC: David Miller <davem at davemloft.net>
> CC: Linus Torvalds <torvalds at linux-foundation.org>
> CC: Andrew Morton <akpm at linux-foundation.org>
> CC: Ingo Molnar <mingo at redhat.com>
> CC: Peter Zijlstra <a.p.zijlstra at chello.nl>
> CC: Thomas Gleixner <tglx at linutronix.de>
> CC: Steven Rostedt <rostedt at goodmis.org>
> CC: linux-arch at vger.kernel.org
> ---
>  include/asm-generic/ltt.h |   53 ++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/ltt.h       |   27 +++++++++++++++++++++++
>  kernel/timer.c            |    2 +
>  3 files changed, 82 insertions(+)
> 
> Index: linux-2.6-lttng/kernel/timer.c
> ===================================================================
> --- linux-2.6-lttng.orig/kernel/timer.c	2008-09-16 14:50:15.000000000 -0400
> +++ linux-2.6-lttng/kernel/timer.c	2008-09-16 14:59:17.000000000 -0400
> @@ -37,6 +37,7 @@
>  #include <linux/delay.h>
>  #include <linux/tick.h>
>  #include <linux/kallsyms.h>
> +#include <linux/ltt.h>
>  
>  #include <asm/uaccess.h>
>  #include <asm/unistd.h>
> @@ -1066,6 +1067,7 @@ void do_timer(unsigned long ticks)
>  {
>  	jiffies_64 += ticks;
>  	update_times(ticks);
> +	ltt_add_timestamp(ticks);
>  }
>  
>  #ifdef __ARCH_WANT_SYS_ALARM
> Index: linux-2.6-lttng/include/linux/ltt.h
> ===================================================================
> --- /dev/null	1970-01-01 00:00:00.000000000 +0000
> +++ linux-2.6-lttng/include/linux/ltt.h	2008-09-16 14:58:47.000000000 -0400
> @@ -0,0 +1,27 @@
> +#ifndef _LINUX_LTT_H
> +#define _LINUX_LTT_H
> +
> +/*
> + * Generic LTT clock.
> + *
> + * Chooses between an architecture specific clock or an atomic logical clock.
> + *
> + * Copyright (C) 2007 Mathieu Desnoyers (mathieu.desnoyers at polymtl.ca)
> + */
> +
> +#ifdef CONFIG_LTT_TIMESTAMP
> +#ifdef CONFIG_HAVE_LTT_CLOCK
> +#include <asm/ltt.h>
> +#else
> +#include <asm-generic/ltt.h>
> +
> +#define ltt_get_timestamp32	ltt_get_timestamp32_generic
> +#define ltt_get_timestamp64	ltt_get_timestamp64_generic
> +#define ltt_add_timestamp	ltt_add_timestamp_generic
> +#define ltt_frequency		ltt_frequency_generic
> +#define ltt_freq_scale		ltt_freq_scale_generic
> +#endif /* CONFIG_HAVE_LTT_CLOCK */
> +#else
> +#define ltt_add_timestamp(ticks)
> +#endif /* CONFIG_LTT_TIMESTAMP */
> +#endif /* _LINUX_LTT_H */
> Index: linux-2.6-lttng/include/asm-generic/ltt.h
> ===================================================================
> --- /dev/null	1970-01-01 00:00:00.000000000 +0000
> +++ linux-2.6-lttng/include/asm-generic/ltt.h	2008-09-16 14:58:47.000000000 -0400
> @@ -0,0 +1,53 @@
> +#ifndef _ASM_GENERIC_LTT_H
> +#define _ASM_GENERIC_LTT_H
> +
> +/*
> + * linux/include/asm-generic/ltt.h
> + *
> + * Copyright (C) 2007 - Mathieu Desnoyers (mathieu.desnoyers at polymtl.ca)
> + *
> + * Generic definitions for LTT
> + * Architectures without TSC
> + */
> +
> +#include <linux/param.h>	/* For HZ */
> +#include <asm/atomic.h>
> +
> +#define LTT_GENERIC_CLOCK_SHIFT 13
> +
> +u64 ltt_read_synthetic_tsc(void);
> +
> +extern atomic_t lttng_generic_clock;
> +
> +static inline u32 ltt_get_timestamp32_generic(void)
> +{
> +	return atomic_add_return(1, &lttng_generic_clock);
> +}
> +
> +static inline u64 ltt_get_timestamp64_generic(void)
> +{
> +	return ltt_read_synthetic_tsc();
> +}
> +
> +static inline void ltt_add_timestamp_generic(unsigned long ticks)
> +{
> +	int old_clock, new_clock;
> +
> +	do {
> +		old_clock = atomic_read(&lttng_generic_clock);
> +		new_clock = (old_clock + (ticks << LTT_GENERIC_CLOCK_SHIFT))
> +			& (~((1 << LTT_GENERIC_CLOCK_SHIFT) - 1));
> +	} while (atomic_cmpxchg(&lttng_generic_clock, old_clock, new_clock)
> +			!= old_clock);
> +}
> +
> +static inline unsigned int ltt_frequency_generic(void)
> +{
> +	return HZ << LTT_GENERIC_CLOCK_SHIFT;
> +}
> +
> +static inline u32 ltt_freq_scale_generic(void)
> +{
> +	return 1;
> +}
> +#endif /* _ASM_GENERIC_LTT_H */
> 

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat at redhat.com