From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
Andrew Morton <akpm@linux-foundation.org>,
Frederic Weisbecker <fweisbec@gmail.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 19/21] tracing: Account for preempt off in preempt_schedule()
Date: Fri, 23 Sep 2011 13:00:48 +0200 [thread overview]
Message-ID: <1316775648.9084.1.camel@twins> (raw)
In-Reply-To: <20110922221029.678324653@goodmis.org>
On Thu, 2011-09-22 at 18:09 -0400, Steven Rostedt wrote:
> plain text document attachment
> (0019-tracing-Account-for-preempt-off-in-preempt_schedule.patch)
> From: Steven Rostedt <srostedt@redhat.com>
>
> The preempt_schedule() uses the preempt_disable_notrace() version
> because it can cause infinite recursion by the function tracer as
> the function tracer uses preempt_enable_notrace() which may call
> back into the preempt_schedule() code as the NEED_RESCHED is still
> set and the PREEMPT_ACTIVE has not been set yet.
>
> See commit: d1f74e20b5b064a130cd0743a256c2d3cfe84010 that made this
> change.
>
> The preemptoff and preemptirqsoff latency tracers require the first
> and last preempt count modifiers to enable tracing. But this skips
> the checks. Since we can not convert them back to the non notrace
> version, we can use the idle() hooks for the latency tracers here.
> That is, the start/stop_critical_timings() works well to manually
> start and stop the latency tracer for preempt off timings.
>
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> ---
> kernel/sched.c | 9 +++++++++
> 1 files changed, 9 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/sched.c b/kernel/sched.c
> index ccacdbd..4b096cc 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -4435,7 +4435,16 @@ asmlinkage void __sched notrace preempt_schedule(void)
>
> do {
> add_preempt_count_notrace(PREEMPT_ACTIVE);
> + /*
> + * The add/subtract must not be traced by the function
> + * tracer. But we still want to account for the
> + * preempt off latency tracer. Since the _notrace versions
> + * of add/subtract skip the accounting for latency tracer
> + * we must force it manually.
> + */
> + start_critical_timings();
> schedule();
> + stop_critical_timings();
> sub_preempt_count_notrace(PREEMPT_ACTIVE);
>
> /*
This won't apply, you're patching ancient code.
Anyway, this all stinks, and reading the changelog of
d1f74e20b5b064a130cd0743a256c2d3cfe84010 and the above just makes me
confused.
next prev parent reply other threads:[~2011-09-23 11:01 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-22 22:09 [PATCH 00/21] [GIT PULL][v3.2] tracing: queued up stuff waiting for k.org to come back on line Steven Rostedt
2011-09-22 22:09 ` [PATCH 01/21] tracing: Clean up tb_fmt to not give faulty compile warning Steven Rostedt
2011-09-22 22:09 ` [PATCH 02/21] Tracepoint: Dissociate from module mutex Steven Rostedt
2011-09-22 22:09 ` [PATCH 03/21] x86: jump_label: arch_jump_label_text_poke_early: add missing __init Steven Rostedt
2011-09-22 22:09 ` [PATCH 04/21] tracing/filter: Use static allocation for filter predicates Steven Rostedt
2011-09-22 22:09 ` [PATCH 05/21] tracing/filter: Separate predicate init and filter addition Steven Rostedt
2011-09-22 22:09 ` [PATCH 06/21] tracing/filter: Remove field_name from filter_pred struct Steven Rostedt
2011-09-22 22:09 ` [PATCH 07/21] tracing/filter: Simplify tracepoint event lookup Steven Rostedt
2011-09-22 22:09 ` [PATCH 08/21] tracing/filter: Unify predicate tree walking, change check_pred_tree Steven Rostedt
2011-09-22 22:09 ` [PATCH 09/21] tracing/filter: Change count_leafs function to use walk_pred_tree Steven Rostedt
2011-09-22 22:09 ` [PATCH 10/21] tracing/filter: Change fold_pred_tree " Steven Rostedt
2011-09-22 22:09 ` [PATCH 11/21] tracing/filter: Change fold_pred " Steven Rostedt
2011-09-22 22:09 ` [PATCH 12/21] tracing/filter: Change filter_match_preds function to use Steven Rostedt
2011-09-22 22:09 ` [PATCH 13/21] tracing/filter: Add startup tests for events filter Steven Rostedt
2011-09-22 22:09 ` [PATCH 14/21] tracing: Add preempt disable for filter self test Steven Rostedt
2011-09-22 22:09 ` [PATCH 15/21] trace: Add a new readonly entry to report total buffer size Steven Rostedt
2011-09-22 22:09 ` [PATCH 16/21] trace: Add ring buffer stats to measure rate of events Steven Rostedt
2011-09-22 22:09 ` [PATCH 17/21] tracing: Add a counter clock for those that do not trust clocks Steven Rostedt
2011-09-22 22:09 ` [PATCH 18/21] tracing: Fix preemptirqsoff tracer to not stop at preempt off Steven Rostedt
2011-09-22 22:09 ` [PATCH 19/21] tracing: Account for preempt off in preempt_schedule() Steven Rostedt
2011-09-23 11:00 ` Peter Zijlstra [this message]
2011-09-23 11:19 ` Steven Rostedt
2011-09-23 11:22 ` Peter Zijlstra
2011-09-23 12:24 ` Steven Rostedt
2011-09-23 14:00 ` Peter Zijlstra
2011-09-23 14:07 ` Peter Zijlstra
2011-09-23 13:24 ` Peter Zijlstra
2011-09-22 22:09 ` [PATCH 20/21] tracing: Do not allocate buffer for trace_marker Steven Rostedt
2011-09-22 22:09 ` [PATCH 21/21] tracing: Add optional percpu buffers for trace_printk() Steven Rostedt
2011-09-23 11:02 ` Peter Zijlstra
2011-09-23 11:07 ` Peter Zijlstra
2011-09-23 11:16 ` Steven Rostedt
2011-09-23 11:28 ` Peter Zijlstra
2011-09-23 11:39 ` Steven Rostedt
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