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    Subject[PATCH 14/20 -v5] Add tracing of context switches
    This patch adds context switch tracing, of the format of:

    _------=> CPU#
    / _-----=> irqs-off
    | / _----=> need-resched
    || / _---=> hardirq/softirq
    ||| / _--=> preempt-depth
    |||| /
    ||||| delay
    cmd pid ||||| time | caller
    \ / ||||| \ | /
    swapper-0 1d..3 137us+: 0:140:R --> 2912:120
    sshd-2912 1d..3 216us+: 2912:120:S --> 0:140
    swapper-0 1d..3 261us+: 0:140:R --> 2912:120
    bash-2920 0d..3 267us+: 2920:120:S --> 0:140
    sshd-2912 1d..3 330us!: 2912:120:S --> 0:140
    swapper-0 1d..3 2389us+: 0:140:R --> 2847:120
    yum-upda-2847 1d..3 2411us!: 2847:120:S --> 0:140
    swapper-0 0d..3 11089us+: 0:140:R --> 3139:120
    gdm-bina-3139 0d..3 11113us!: 3139:120:S --> 0:140
    swapper-0 1d..3 102328us+: 0:140:R --> 2847:120
    yum-upda-2847 1d..3 102348us!: 2847:120:S --> 0:140


    "sched_switch" is added to /debugfs/tracing/available_tracers

    Signed-off-by: Steven Rostedt <srostedt@redhat.com>
    Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
    ---
    lib/tracing/Kconfig | 9 ++
    lib/tracing/Makefile | 1
    lib/tracing/trace_sched_switch.c | 134 +++++++++++++++++++++++++++++++++++++++
    lib/tracing/tracer.c | 32 +++++++++
    lib/tracing/tracer.h | 19 +++++
    5 files changed, 194 insertions(+), 1 deletion(-)

    Index: linux-mcount.git/lib/tracing/Kconfig
    ===================================================================
    --- linux-mcount.git.orig/lib/tracing/Kconfig 2008-01-23 10:27:19.000000000 -0500
    +++ linux-mcount.git/lib/tracing/Kconfig 2008-01-23 10:27:31.000000000 -0500
    @@ -23,3 +23,12 @@ config FUNCTION_TRACER
    insert a call to an architecture specific __mcount routine,
    that the debugging mechanism using this facility will hook by
    providing a set of inline routines.
    +
    +config CONTEXT_SWITCH_TRACER
    + bool "Trace process context switches"
    + depends on DEBUG_KERNEL
    + select TRACING
    + help
    + This tracer hooks into the context switch and records
    + all switching of tasks.
    +
    Index: linux-mcount.git/lib/tracing/Makefile
    ===================================================================
    --- linux-mcount.git.orig/lib/tracing/Makefile 2008-01-23 10:27:19.000000000 -0500
    +++ linux-mcount.git/lib/tracing/Makefile 2008-01-23 10:27:31.000000000 -0500
    @@ -1,6 +1,7 @@
    obj-$(CONFIG_MCOUNT) += libmcount.o

    obj-$(CONFIG_TRACING) += tracer.o
    +obj-$(CONFIG_CONTEXT_SWITCH_TRACER) += trace_sched_switch.o
    obj-$(CONFIG_FUNCTION_TRACER) += trace_function.o

    libmcount-y := mcount.o
    Index: linux-mcount.git/lib/tracing/trace_sched_switch.c
    ===================================================================
    --- /dev/null 1970-01-01 00:00:00.000000000 +0000
    +++ linux-mcount.git/lib/tracing/trace_sched_switch.c 2008-01-23 10:27:31.000000000 -0500
    @@ -0,0 +1,134 @@
    +/*
    + * trace context switch
    + *
    + * Copyright (C) 2007 Steven Rostedt <srostedt@redhat.com>
    + *
    + */
    +#include <linux/module.h>
    +#include <linux/fs.h>
    +#include <linux/debugfs.h>
    +#include <linux/kallsyms.h>
    +#include <linux/uaccess.h>
    +#include <linux/marker.h>
    +#include <linux/mcount.h>
    +
    +#include "tracer.h"
    +
    +static struct tracing_trace *tracer_trace;
    +static int trace_enabled __read_mostly;
    +
    +static notrace void sched_switch_callback(const struct marker *mdata,
    + void *private_data,
    + const char *format, ...)
    +{
    + struct tracing_trace **p = mdata->private;
    + struct tracing_trace *tr = *p;
    + struct tracing_trace_cpu *data;
    + struct task_struct *prev;
    + struct task_struct *next;
    + unsigned long flags;
    + va_list ap;
    + int cpu;
    +
    + if (likely(!trace_enabled))
    + return;
    +
    + va_start(ap, format);
    + prev = va_arg(ap, typeof(prev));
    + next = va_arg(ap, typeof(next));
    + va_end(ap);
    +
    + raw_local_irq_save(flags);
    + cpu = raw_smp_processor_id();
    + data = tr->data[cpu];
    + atomic_inc(&data->disabled);
    +
    + if (likely(atomic_read(&data->disabled) == 1))
    + tracing_sched_switch_trace(tr, data, prev, next, flags);
    +
    + atomic_dec(&data->disabled);
    + raw_local_irq_restore(flags);
    +}
    +
    +static notrace void sched_switch_reset(struct tracing_trace *tr)
    +{
    + int cpu;
    +
    + tr->time_start = now();
    +
    + for_each_online_cpu(cpu)
    + tracing_reset(tr->data[cpu]);
    +}
    +
    +static notrace void start_sched_trace(struct tracing_trace *tr)
    +{
    + sched_switch_reset(tr);
    + trace_enabled = 1;
    +}
    +
    +static notrace void stop_sched_trace(struct tracing_trace *tr)
    +{
    + trace_enabled = 0;
    +}
    +
    +static notrace void sched_switch_trace_init(struct tracing_trace *tr)
    +{
    + tracer_trace = tr;
    +
    + if (tr->ctrl)
    + start_sched_trace(tr);
    +}
    +
    +static notrace void sched_switch_trace_reset(struct tracing_trace *tr)
    +{
    + if (tr->ctrl)
    + stop_sched_trace(tr);
    +}
    +
    +static void sched_switch_trace_ctrl_update(struct tracing_trace *tr)
    +{
    + /* When starting a new trace, reset the buffers */
    + if (tr->ctrl)
    + start_sched_trace(tr);
    + else
    + stop_sched_trace(tr);
    +}
    +
    +static struct trace_types_struct sched_switch_trace __read_mostly =
    +{
    + .name = "sched_switch",
    + .init = sched_switch_trace_init,
    + .reset = sched_switch_trace_reset,
    + .ctrl_update = sched_switch_trace_ctrl_update,
    +};
    +
    +
    +__init static int init_sched_switch_trace(void)
    +{
    + int ret;
    +
    + ret = register_trace(&sched_switch_trace);
    + if (ret)
    + return ret;
    +
    + ret = marker_probe_register("kernel_sched_schedule",
    + "prev %p next %p",
    + sched_switch_callback,
    + &tracer_trace);
    + if (ret) {
    + pr_info("sched trace: Couldn't add marker"
    + " probe to switch_to\n");
    + goto out;
    + }
    +
    + ret = marker_arm("kernel_sched_schedule");
    + if (ret) {
    + pr_info("sched trace: Couldn't arm probe switch_to\n");
    + goto out;
    + }
    +
    + out:
    + return ret;
    +}
    +
    +device_initcall(init_sched_switch_trace);
    Index: linux-mcount.git/lib/tracing/tracer.c
    ===================================================================
    --- linux-mcount.git.orig/lib/tracing/tracer.c 2008-01-23 10:27:19.000000000 -0500
    +++ linux-mcount.git/lib/tracing/tracer.c 2008-01-23 10:27:31.000000000 -0500
    @@ -52,6 +52,7 @@ enum trace_type {
    __TRACE_FIRST_TYPE = 0,

    TRACE_FN,
    + TRACE_CTX,

    __TRACE_LAST_TYPE
    };
    @@ -227,6 +228,24 @@ notrace void tracing_function_trace(stru
    entry->fn.parent_ip = parent_ip;
    }

    +notrace void tracing_sched_switch_trace(struct tracing_trace *tr,
    + struct tracing_trace_cpu *data,
    + struct task_struct *prev,
    + struct task_struct *next,
    + unsigned long flags)
    +{
    + struct tracing_entry *entry;
    +
    + entry = tracing_get_trace_entry(tr, data);
    + tracing_generic_entry_update(entry, flags);
    + entry->type = TRACE_CTX;
    + entry->ctx.prev_pid = prev->pid;
    + entry->ctx.prev_prio = prev->prio;
    + entry->ctx.prev_state = prev->state;
    + entry->ctx.next_pid = next->pid;
    + entry->ctx.next_prio = next->prio;
    +}
    +
    enum trace_iterator {
    TRACE_ITER_SYM_ONLY = 1,
    TRACE_ITER_VERBOSE = 2,
    @@ -545,6 +564,8 @@ lat_print_timestamp(struct seq_file *m,
    seq_puts(m, " : ");
    }

    +static const char state_to_char[] = TASK_STATE_TO_CHAR_STR;
    +
    static void notrace
    print_lat_fmt(struct seq_file *m, struct tracing_iterator *iter,
    unsigned int trace_idx, int cpu)
    @@ -555,6 +576,7 @@ print_lat_fmt(struct seq_file *m, struct
    unsigned long rel_usecs;
    int sym_only = !!(trace_flags & TRACE_ITER_SYM_ONLY);
    int verbose = !!(trace_flags & TRACE_ITER_VERBOSE);
    + int S;

    if (!next_entry)
    next_entry = entry;
    @@ -581,6 +603,16 @@ print_lat_fmt(struct seq_file *m, struct
    seq_print_ip_sym(m, entry->fn.parent_ip, sym_only);
    seq_puts(m, ")\n");
    break;
    + case TRACE_CTX:
    + S = entry->ctx.prev_state < sizeof(state_to_char) ?
    + state_to_char[entry->ctx.prev_state] : 'X';
    + seq_printf(m, " %d:%d:%c --> %d:%d\n",
    + entry->ctx.prev_pid,
    + entry->ctx.prev_prio,
    + S,
    + entry->ctx.next_pid,
    + entry->ctx.next_prio);
    + break;
    }
    }

    Index: linux-mcount.git/lib/tracing/tracer.h
    ===================================================================
    --- linux-mcount.git.orig/lib/tracing/tracer.h 2008-01-23 10:27:19.000000000 -0500
    +++ linux-mcount.git/lib/tracing/tracer.h 2008-01-23 10:27:31.000000000 -0500
    @@ -10,6 +10,14 @@ struct tracing_function {
    unsigned long parent_ip;
    };

    +struct tracing_sched_switch {
    + unsigned int prev_pid;
    + unsigned char prev_prio;
    + unsigned char prev_state;
    + unsigned int next_pid;
    + unsigned char next_prio;
    +};
    +
    struct tracing_entry {
    char type;
    char cpu; /* who will want to trace more than 256 CPUS? */
    @@ -18,7 +26,10 @@ struct tracing_entry {
    int pid;
    cycle_t t;
    char comm[TASK_COMM_LEN];
    - struct tracing_function fn;
    + union {
    + struct tracing_function fn;
    + struct tracing_sched_switch ctx;
    + };
    };

    struct tracing_trace_cpu {
    @@ -82,6 +93,12 @@ void tracing_function_trace(struct traci
    unsigned long ip,
    unsigned long parent_ip,
    unsigned long flags);
    +void tracing_sched_switch_trace(struct tracing_trace *tr,
    + struct tracing_trace_cpu *data,
    + struct task_struct *prev,
    + struct task_struct *next,
    + unsigned long flags);
    +

    void tracing_start_function_trace(void);
    void tracing_stop_function_trace(void);
    --


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