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    Subject[PATCH 3/7] tracing: Reduce latency and remove percpu trace_seq
    From: Lai Jiangshan <laijs@cn.fujitsu.com>

    __print_flags() and __print_symbolic() use percpu trace_seq:

    1) Its memory is allocated at compile time, it wastes memory if we don't use tracing.
    2) It is percpu data and it wastes more memory for multi-cpus system.
    3) It disables preemption when it executes its core routine
    "trace_seq_printf(s, "%s: ", #call);" and introduces latency.

    So we move this trace_seq to struct trace_iterator.

    Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
    LKML-Reference: <4C078350.7090106@cn.fujitsu.com>
    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
    ---
    include/linux/ftrace_event.h | 5 +++--
    include/trace/ftrace.h | 12 +++---------
    kernel/trace/trace_output.c | 3 ---
    3 files changed, 6 insertions(+), 14 deletions(-)

    diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
    index 2b7b139..02b8b24 100644
    --- a/include/linux/ftrace_event.h
    +++ b/include/linux/ftrace_event.h
    @@ -11,8 +11,6 @@ struct trace_array;
    struct tracer;
    struct dentry;

    -DECLARE_PER_CPU(struct trace_seq, ftrace_event_seq);
    -
    struct trace_print_flags {
    unsigned long mask;
    const char *name;
    @@ -58,6 +56,9 @@ struct trace_iterator {
    struct ring_buffer_iter *buffer_iter[NR_CPUS];
    unsigned long iter_flags;

    + /* trace_seq for __print_flags() and __print_symbolic() etc. */
    + struct trace_seq tmp_seq;
    +
    /* The below is zeroed out in pipe_read */
    struct trace_seq seq;
    struct trace_entry *ent;
    diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
    index 55c1fd1..fb783d9 100644
    --- a/include/trace/ftrace.h
    +++ b/include/trace/ftrace.h
    @@ -145,7 +145,7 @@
    * struct trace_seq *s = &iter->seq;
    * struct ftrace_raw_<call> *field; <-- defined in stage 1
    * struct trace_entry *entry;
    - * struct trace_seq *p;
    + * struct trace_seq *p = &iter->tmp_seq;
    * int ret;
    *
    * entry = iter->ent;
    @@ -157,12 +157,10 @@
    *
    * field = (typeof(field))entry;
    *
    - * p = &get_cpu_var(ftrace_event_seq);
    * trace_seq_init(p);
    * ret = trace_seq_printf(s, "%s: ", <call>);
    * if (ret)
    * ret = trace_seq_printf(s, <TP_printk> "\n");
    - * put_cpu();
    * if (!ret)
    * return TRACE_TYPE_PARTIAL_LINE;
    *
    @@ -216,7 +214,7 @@ ftrace_raw_output_##call(struct trace_iterator *iter, int flags, \
    struct trace_seq *s = &iter->seq; \
    struct ftrace_raw_##call *field; \
    struct trace_entry *entry; \
    - struct trace_seq *p; \
    + struct trace_seq *p = &iter->tmp_seq; \
    int ret; \
    \
    event = container_of(trace_event, struct ftrace_event_call, \
    @@ -231,12 +229,10 @@ ftrace_raw_output_##call(struct trace_iterator *iter, int flags, \
    \
    field = (typeof(field))entry; \
    \
    - p = &get_cpu_var(ftrace_event_seq); \
    trace_seq_init(p); \
    ret = trace_seq_printf(s, "%s: ", event->name); \
    if (ret) \
    ret = trace_seq_printf(s, print); \
    - put_cpu(); \
    if (!ret) \
    return TRACE_TYPE_PARTIAL_LINE; \
    \
    @@ -255,7 +251,7 @@ ftrace_raw_output_##call(struct trace_iterator *iter, int flags, \
    struct trace_seq *s = &iter->seq; \
    struct ftrace_raw_##template *field; \
    struct trace_entry *entry; \
    - struct trace_seq *p; \
    + struct trace_seq *p = &iter->tmp_seq; \
    int ret; \
    \
    entry = iter->ent; \
    @@ -267,12 +263,10 @@ ftrace_raw_output_##call(struct trace_iterator *iter, int flags, \
    \
    field = (typeof(field))entry; \
    \
    - p = &get_cpu_var(ftrace_event_seq); \
    trace_seq_init(p); \
    ret = trace_seq_printf(s, "%s: ", #call); \
    if (ret) \
    ret = trace_seq_printf(s, print); \
    - put_cpu(); \
    if (!ret) \
    return TRACE_TYPE_PARTIAL_LINE; \
    \
    diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
    index 57c1b45..1ba64d3 100644
    --- a/kernel/trace/trace_output.c
    +++ b/kernel/trace/trace_output.c
    @@ -16,9 +16,6 @@

    DECLARE_RWSEM(trace_event_mutex);

    -DEFINE_PER_CPU(struct trace_seq, ftrace_event_seq);
    -EXPORT_PER_CPU_SYMBOL(ftrace_event_seq);
    -
    static struct hlist_head event_hash[EVENT_HASHSIZE] __read_mostly;

    static int next_event_type = __TRACE_LAST_TYPE + 1;
    --
    1.7.1



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