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Message-Id: <1216197251.5232.21.camel@twins>
Date: Wed, 16 Jul 2008 10:34:11 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc: akpm@...ux-foundation.org, Ingo Molnar <mingo@...e.hu>,
linux-kernel@...r.kernel.org,
Masami Hiramatsu <mhiramat@...hat.com>,
"David S. Miller" <davem@...emloft.net>,
"Frank Ch. Eigler" <fche@...hat.com>,
Hideo AOKI <haoki@...hat.com>,
Takashi Nishiie <t-nishiie@...css.fujitsu.com>,
Steven Rostedt <rostedt@...dmis.org>,
Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 07/17] LTTng instrumentation - timer
On Tue, 2008-07-15 at 18:26 -0400, Mathieu Desnoyers wrote:
> plain text document attachment (lttng-instrumentation-timer.patch)
> Instrument timer activity (timer set, expired, current time updates) to keep
> information about the "real time" flow within the kernel. It can be used by a
> trace analysis tool to synchronize information coming from various sources, e.g.
> to merge traces with system logs.
>
> Those tracepoints are used by LTTng.
>
> About the performance impact of tracepoints (which is comparable to markers),
> even without immediate values optimizations, tests done by Hideo Aoki on ia64
> show no regression. His test case was using hackbench on a kernel where
> scheduler instrumentation (about 5 events in code scheduler code) was added.
> See the "Tracepoints" patch header for performance result detail.
>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
> CC: 'Ingo Molnar' <mingo@...e.hu>
> CC: "David S. Miller" <davem@...emloft.net>
> CC: Masami Hiramatsu <mhiramat@...hat.com>
> CC: 'Peter Zijlstra' <peterz@...radead.org>
> CC: "Frank Ch. Eigler" <fche@...hat.com>
> CC: 'Hideo AOKI' <haoki@...hat.com>
> CC: Takashi Nishiie <t-nishiie@...css.fujitsu.com>
> CC: 'Steven Rostedt' <rostedt@...dmis.org>
> CC: Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
> ---
> include/trace/timer.h | 24 ++++++++++++++++++++++++
> kernel/itimer.c | 5 +++++
> kernel/timer.c | 8 +++++++-
> 3 files changed, 36 insertions(+), 1 deletion(-)
>
> Index: linux-2.6-lttng/kernel/itimer.c
> ===================================================================
> --- linux-2.6-lttng.orig/kernel/itimer.c 2008-07-15 14:49:14.000000000 -0400
> +++ linux-2.6-lttng/kernel/itimer.c 2008-07-15 15:14:28.000000000 -0400
> @@ -12,6 +12,7 @@
> #include <linux/time.h>
> #include <linux/posix-timers.h>
> #include <linux/hrtimer.h>
> +#include <trace/timer.h>
>
> #include <asm/uaccess.h>
>
> @@ -132,6 +133,8 @@ enum hrtimer_restart it_real_fn(struct h
> struct signal_struct *sig =
> container_of(timer, struct signal_struct, real_timer);
>
> + trace_timer_itimer_expired(sig);
> +
> kill_pid_info(SIGALRM, SEND_SIG_PRIV, sig->leader_pid);
>
> return HRTIMER_NORESTART;
> @@ -157,6 +160,8 @@ int do_setitimer(int which, struct itime
> !timeval_valid(&value->it_interval))
> return -EINVAL;
>
> + trace_timer_itimer_set(which, value);
> +
> switch (which) {
> case ITIMER_REAL:
> again:
> Index: linux-2.6-lttng/kernel/timer.c
> ===================================================================
> --- linux-2.6-lttng.orig/kernel/timer.c 2008-07-15 14:51:50.000000000 -0400
> +++ linux-2.6-lttng/kernel/timer.c 2008-07-15 15:14:28.000000000 -0400
> @@ -37,12 +37,14 @@
> #include <linux/delay.h>
> #include <linux/tick.h>
> #include <linux/kallsyms.h>
> +#include <trace/timer.h>
>
> #include <asm/uaccess.h>
> #include <asm/unistd.h>
> #include <asm/div64.h>
> #include <asm/timex.h>
> #include <asm/io.h>
> +#include <asm/irq_regs.h>
>
> u64 jiffies_64 __cacheline_aligned_in_smp = INITIAL_JIFFIES;
>
> @@ -288,6 +290,7 @@ static void internal_add_timer(struct tv
> i = (expires >> (TVR_BITS + 3 * TVN_BITS)) & TVN_MASK;
> vec = base->tv5.vec + i;
> }
> + trace_timer_set(timer);
> /*
> * Timers are FIFO:
> */
> @@ -1066,6 +1069,7 @@ void do_timer(unsigned long ticks)
> {
> jiffies_64 += ticks;
> update_times(ticks);
> + trace_timer_update_time(&xtime, &wall_to_monotonic);
> }
This is a very dangerous trace point - we're holding xtime lock here.
Ah, I see you make that comment below too, are you sure you want to do
this?
Thomas, any input?
> #ifdef __ARCH_WANT_SYS_ALARM
> @@ -1147,7 +1151,9 @@ asmlinkage long sys_getegid(void)
>
> static void process_timeout(unsigned long __data)
> {
> - wake_up_process((struct task_struct *)__data);
> + struct task_struct *task = (struct task_struct *)__data;
> + trace_timer_timeout(task);
> + wake_up_process(task);
> }
>
> /**
> Index: linux-2.6-lttng/include/trace/timer.h
> ===================================================================
> --- /dev/null 1970-01-01 00:00:00.000000000 +0000
> +++ linux-2.6-lttng/include/trace/timer.h 2008-07-15 15:14:28.000000000 -0400
> @@ -0,0 +1,24 @@
> +#ifndef _TRACE_TIMER_H
> +#define _TRACE_TIMER_H
> +
> +#include <linux/tracepoint.h>
> +
> +DEFINE_TRACE(timer_itimer_expired,
> + TPPROTO(struct signal_struct *sig),
> + TPARGS(sig));
> +DEFINE_TRACE(timer_itimer_set,
> + TPPROTO(int which, struct itimerval *value),
> + TPARGS(which, value));
> +DEFINE_TRACE(timer_set,
> + TPPROTO(struct timer_list *timer),
> + TPARGS(timer));
> +/*
> + * xtime_lock is taken when kernel_timer_update_time tracepoint is reached.
> + */
> +DEFINE_TRACE(timer_update_time,
> + TPPROTO(struct timespec *_xtime, struct timespec *_wall_to_monotonic),
> + TPARGS(_xtime, _wall_to_monotonic));
> +DEFINE_TRACE(timer_timeout,
> + TPPROTO(struct task_struct *p),
> + TPARGS(p));
> +#endif
>
--
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