On Fri, Oct 04, 2013 at 10:53:42AM -0400, Steven Rostedt wrote:
> In other words, what does these flags in the trace actually mean?
> Probably need to add comments in the code and/or update the
> Documentation section
If "task need resched" is supposed to explain things; the below too will
suffice... muwhahaha!
---
Subject: ftrace, sched: Add TRACE_FLAG_PREEMPT_RESCHED
From: Peter Zijlstra <pet...@infradead.org>
Date: Fri Sep 27 17:11:00 CEST 2013
Since the introduction of PREEMPT_NEED_RESCHED; see commit:
f27dde8deef3 ("sched: Add NEED_RESCHED to the preempt_count") we need
to be able to look at both TIF_NEED_RESCHED and PREEMPT_NEED_RESCHED
to understand the full preemption behaviour. Add it to the trace
output.
Cc: Steven Rostedt <rost...@goodmis.org>
Signed-off-by: Peter Zijlstra <pet...@infradead.org>
Link: http://lkml.kernel.org/n/tip-1tys5rfpbpi7ky20b7msh...@git.kernel.org
---
Documentation/trace/ftrace.txt | 6 +++++-
kernel/trace/trace.c | 3 ++-
kernel/trace/trace.h | 1 +
kernel/trace/trace_output.c | 13 +++++++++++--
4 files changed, 19 insertions(+), 4 deletions(-)
--- a/Documentation/trace/ftrace.txt
+++ b/Documentation/trace/ftrace.txt
@@ -655,7 +655,11 @@ explains which is which.
read the irq flags variable, an 'X' will always
be printed here.
- need-resched: 'N' task need_resched is set, '.' otherwise.
+ need-resched:
+ 'N' both TIF_NEED_RESCHED and PREEMPT_NEED_RESCHED is set,
+ 'n' only TIF_NEED_RESCHED is set,
+ 'p' only PREEMPT_NEED_RESCHED is set,
+ '.' otherwise.
hardirq/softirq:
'H' - hard irq occurred inside a softirq.
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1509,7 +1509,8 @@ tracing_generic_entry_update(struct trac
#endif
((pc & HARDIRQ_MASK) ? TRACE_FLAG_HARDIRQ : 0) |
((pc & SOFTIRQ_MASK) ? TRACE_FLAG_SOFTIRQ : 0) |
- (need_resched() ? TRACE_FLAG_NEED_RESCHED : 0);
+ (tif_need_resched() ? TRACE_FLAG_NEED_RESCHED : 0) |
+ (test_preempt_need_resched() ? TRACE_FLAG_PREEMPT_RESCHED : 0);
}
EXPORT_SYMBOL_GPL(tracing_generic_entry_update);
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -124,6 +124,7 @@ enum trace_flag_type {
TRACE_FLAG_NEED_RESCHED = 0x04,
TRACE_FLAG_HARDIRQ = 0x08,
TRACE_FLAG_SOFTIRQ = 0x10,
+ TRACE_FLAG_PREEMPT_RESCHED = 0x20,
};
#define TRACE_BUF_SIZE 1024
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -618,8 +618,17 @@ int trace_print_lat_fmt(struct trace_seq
(entry->flags & TRACE_FLAG_IRQS_OFF) ? 'd' :
(entry->flags & TRACE_FLAG_IRQS_NOSUPPORT) ? 'X' :
'.';
- need_resched =
- (entry->flags & TRACE_FLAG_NEED_RESCHED) ? 'N' : '.';
+
+ if ((entry->flags & TRACE_FLAG_NEED_RESCHED) &&
+ (entry->flags & TRACE_FLAG_PREEMPT_RESCHED))
+ need_resched = 'N';
+ else if (entry->flags & TRACE_FLAG_NEED_RESCHED)
+ need_resched = 'n';
+ else if (entry->flags & TRACE_FLAG_PREEMPT_RESCHED)
+ need_resched = 'p';
+ else
+ need_resched = '.';
+
hardsoft_irq =
(hardirq && softirq) ? 'H' :
hardirq ? 'h' :
--
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