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    Subject[tip:sched/core] ftrace, sched: Add TRACE_FLAG_PREEMPT_RESCHED
    Commit-ID:  e5137b50a0640009fd63a3e65c14bc6e1be8796a
    Gitweb: http://git.kernel.org/tip/e5137b50a0640009fd63a3e65c14bc6e1be8796a
    Author: Peter Zijlstra <peterz@infradead.org>
    AuthorDate: Fri, 4 Oct 2013 17:28:26 +0200
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Mon, 11 Nov 2013 12:43:39 +0100

    ftrace, sched: Add TRACE_FLAG_PREEMPT_RESCHED

    Since the introduction of PREEMPT_NEED_RESCHED in:

    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.

    Signed-off-by: Peter Zijlstra <peterz@infradead.org>
    Acked-by: Steven Rostedt <rostedt@goodmis.org>
    Cc: Fengguang Wu <fengguang.wu@intel.com>
    Cc: Huang Ying <ying.huang@intel.com>
    Cc: Yuanhan Liu <yuanhan.liu@linux.intel.com>
    Link: http://lkml.kernel.org/r/20131004152826.GP3081@twins.programming.kicks-ass.net
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    Documentation/trace/ftrace.txt | 6 +++++-
    kernel/trace/trace.c | 3 ++-
    kernel/trace/trace.h | 1 +
    kernel/trace/trace_output.c | 19 +++++++++++++++++--
    4 files changed, 25 insertions(+), 4 deletions(-)

    diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt
    index ea2d35d..bd36598 100644
    --- 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.
    diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
    index 7974ba2..d9fea7d 100644
    --- a/kernel/trace/trace.c
    +++ b/kernel/trace/trace.c
    @@ -1509,7 +1509,8 @@ tracing_generic_entry_update(struct trace_entry *entry, unsigned long flags,
    #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);

    diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
    index 10c86fb..73d08aa 100644
    --- 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
    diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
    index 34e7cba..ed32284 100644
    --- a/kernel/trace/trace_output.c
    +++ b/kernel/trace/trace_output.c
    @@ -618,8 +618,23 @@ int trace_print_lat_fmt(struct trace_seq *s, struct trace_entry *entry)
    (entry->flags & TRACE_FLAG_IRQS_OFF) ? 'd' :
    (entry->flags & TRACE_FLAG_IRQS_NOSUPPORT) ? 'X' :
    '.';
    - need_resched =
    - (entry->flags & TRACE_FLAG_NEED_RESCHED) ? 'N' : '.';
    +
    + switch (entry->flags & (TRACE_FLAG_NEED_RESCHED |
    + TRACE_FLAG_PREEMPT_RESCHED)) {
    + case TRACE_FLAG_NEED_RESCHED | TRACE_FLAG_PREEMPT_RESCHED:
    + need_resched = 'N';
    + break;
    + case TRACE_FLAG_NEED_RESCHED:
    + need_resched = 'n';
    + break;
    + case TRACE_FLAG_PREEMPT_RESCHED:
    + need_resched = 'p';
    + break;
    + default:
    + need_resched = '.';
    + break;
    + }
    +
    hardsoft_irq =
    (hardirq && softirq) ? 'H' :
    hardirq ? 'h' :

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