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    Subject[PATCH 15/20 -v5] Generic command line storage
    Saving the comm of tasks for each trace is very expensive.
    This patch includes in the context switch hook, a way to
    store the last 100 command lines of tasks. This table is
    examined when a trace is to be printed.

    Note: The comm may be destroyed if other traces are performed.
    Later (TBD) patches may simply store this information in the trace
    itself.

    Signed-off-by: Steven Rostedt <srostedt@redhat.com>
    ---
    lib/tracing/Kconfig | 1
    lib/tracing/trace_function.c | 2
    lib/tracing/trace_sched_switch.c | 7 ++
    lib/tracing/tracer.c | 104 +++++++++++++++++++++++++++++++++++++--
    lib/tracing/tracer.h | 6 +-
    5 files changed, 114 insertions(+), 6 deletions(-)
    Index: linux-mcount.git/lib/tracing/Kconfig
    ===================================================================
    --- linux-mcount.git.orig/lib/tracing/Kconfig 2008-01-23 10:27:31.000000000 -0500
    +++ linux-mcount.git/lib/tracing/Kconfig 2008-01-23 10:27:39.000000000 -0500
    @@ -18,6 +18,7 @@ config FUNCTION_TRACER
    depends on DEBUG_KERNEL && HAVE_MCOUNT
    select MCOUNT
    select TRACING
    + select CONTEXT_SWITCH_TRACER
    help
    Use profiler instrumentation, adding -pg to CFLAGS. This will
    insert a call to an architecture specific __mcount routine,
    Index: linux-mcount.git/lib/tracing/trace_function.c
    ===================================================================
    --- linux-mcount.git.orig/lib/tracing/trace_function.c 2008-01-23 10:27:19.000000000 -0500
    +++ linux-mcount.git/lib/tracing/trace_function.c 2008-01-23 10:27:39.000000000 -0500
    @@ -28,11 +28,13 @@ static notrace void function_reset(struc
    static notrace void start_function_trace(struct tracing_trace *tr)
    {
    function_reset(tr);
    + atomic_inc(&trace_record_cmdline);
    tracing_start_function_trace();
    }

    static notrace void stop_function_trace(struct tracing_trace *tr)
    {
    + atomic_dec(&trace_record_cmdline);
    tracing_stop_function_trace();
    }

    Index: linux-mcount.git/lib/tracing/trace_sched_switch.c
    ===================================================================
    --- linux-mcount.git.orig/lib/tracing/trace_sched_switch.c 2008-01-23 10:27:31.000000000 -0500
    +++ linux-mcount.git/lib/tracing/trace_sched_switch.c 2008-01-23 10:27:39.000000000 -0500
    @@ -30,6 +30,11 @@ static notrace void sched_switch_callbac
    va_list ap;
    int cpu;

    + if (likely(!atomic_read(&trace_record_cmdline)))
    + return;
    +
    + tracing_record_cmdline(current);
    +
    if (likely(!trace_enabled))
    return;

    @@ -62,6 +67,7 @@ static notrace void sched_switch_reset(s

    static notrace void start_sched_trace(struct tracing_trace *tr)
    {
    + atomic_inc(&trace_record_cmdline);
    sched_switch_reset(tr);
    trace_enabled = 1;
    }
    @@ -69,6 +75,7 @@ static notrace void start_sched_trace(st
    static notrace void stop_sched_trace(struct tracing_trace *tr)
    {
    trace_enabled = 0;
    + atomic_dec(&trace_record_cmdline);
    }

    static notrace void sched_switch_trace_init(struct tracing_trace *tr)
    Index: linux-mcount.git/lib/tracing/tracer.c
    ===================================================================
    --- linux-mcount.git.orig/lib/tracing/tracer.c 2008-01-23 10:27:31.000000000 -0500
    +++ linux-mcount.git/lib/tracing/tracer.c 2008-01-23 10:27:39.000000000 -0500
    @@ -169,6 +169,88 @@ void tracing_stop_function_trace(void)
    unregister_mcount_function(&trace_ops);
    }

    +#define SAVED_CMDLINES 128
    +static unsigned map_pid_to_cmdline[PID_MAX_DEFAULT+1];
    +static unsigned map_cmdline_to_pid[SAVED_CMDLINES];
    +static char saved_cmdlines[SAVED_CMDLINES][TASK_COMM_LEN];
    +static int cmdline_idx;
    +static DEFINE_SPINLOCK(trace_cmdline_lock);
    +atomic_t trace_record_cmdline;
    +atomic_t trace_record_cmdline_disabled;
    +
    +static void trace_init_cmdlines(void)
    +{
    + memset(&map_pid_to_cmdline, -1, sizeof(map_pid_to_cmdline));
    + memset(&map_cmdline_to_pid, -1, sizeof(map_cmdline_to_pid));
    + cmdline_idx = 0;
    +}
    +
    +notrace void trace_stop_cmdline_recording(void);
    +
    +static void notrace trace_save_cmdline(struct task_struct *tsk)
    +{
    + unsigned map;
    + unsigned idx;
    +
    + if (!tsk->pid || unlikely(tsk->pid > PID_MAX_DEFAULT))
    + return;
    +
    + /*
    + * It's not the end of the world if we don't get
    + * the lock, but we also don't want to spin
    + * nor do we want to disable interrupts,
    + * so if we miss here, then better luck next time.
    + */
    + if (!spin_trylock(&trace_cmdline_lock))
    + return;
    +
    + idx = map_pid_to_cmdline[tsk->pid];
    + if (idx >= SAVED_CMDLINES) {
    + idx = (cmdline_idx + 1) % SAVED_CMDLINES;
    +
    + map = map_cmdline_to_pid[idx];
    + if (map <= PID_MAX_DEFAULT)
    + map_pid_to_cmdline[map] = (unsigned)-1;
    +
    + map_pid_to_cmdline[tsk->pid] = idx;
    +
    + cmdline_idx = idx;
    + }
    +
    + memcpy(&saved_cmdlines[idx], tsk->comm, TASK_COMM_LEN);
    +
    + spin_unlock(&trace_cmdline_lock);
    +}
    +
    +static notrace char *trace_find_cmdline(int pid)
    +{
    + char *cmdline = "<...>";
    + unsigned map;
    +
    + if (!pid)
    + return "<idle>";
    +
    + if (pid > PID_MAX_DEFAULT)
    + goto out;
    +
    + map = map_pid_to_cmdline[pid];
    + if (map >= SAVED_CMDLINES)
    + goto out;
    +
    + cmdline = saved_cmdlines[map];
    +
    + out:
    + return cmdline;
    +}
    +
    +void tracing_record_cmdline(struct task_struct *tsk)
    +{
    + if (atomic_read(&trace_record_cmdline_disabled))
    + return;
    +
    + trace_save_cmdline(tsk);
    +}
    +
    static inline notrace struct tracing_entry *
    tracing_get_trace_entry(struct tracing_trace *tr,
    struct tracing_trace_cpu *data)
    @@ -210,7 +292,6 @@ tracing_generic_entry_update(struct trac
    ((pc & HARDIRQ_MASK) ? TRACE_FLAG_HARDIRQ : 0) |
    ((pc & SOFTIRQ_MASK) ? TRACE_FLAG_SOFTIRQ : 0) |
    (need_resched() ? TRACE_FLAG_NEED_RESCHED : 0);
    - memcpy(entry->comm, tsk->comm, TASK_COMM_LEN);
    }

    notrace void tracing_function_trace(struct tracing_trace *tr,
    @@ -366,6 +447,8 @@ static void *s_start(struct seq_file *m,
    if (!current_trace || current_trace != iter->trace)
    return NULL;

    + atomic_inc(&trace_record_cmdline_disabled);
    +
    /* let the tracer grab locks here if needed */
    if (current_trace->start)
    current_trace->start(iter);
    @@ -393,6 +476,8 @@ static void s_stop(struct seq_file *m, v
    {
    struct tracing_iterator *iter = m->private;

    + atomic_dec(&trace_record_cmdline_disabled);
    +
    /* let the tracer release locks here if needed */
    if (current_trace && current_trace == iter->trace && iter->trace->stop)
    iter->trace->stop(iter);
    @@ -521,8 +606,11 @@ static void notrace
    lat_print_generic(struct seq_file *m, struct tracing_entry *entry, int cpu)
    {
    int hardirq, softirq;
    + char *comm;
    +
    + comm = trace_find_cmdline(entry->pid);

    - seq_printf(m, "%8.8s-%-5d ", entry->comm, entry->pid);
    + seq_printf(m, "%8.8s-%-5d ", comm, entry->pid);
    seq_printf(m, "%d", cpu);
    seq_printf(m, "%c%c",
    (entry->flags & TRACE_FLAG_IRQS_OFF) ? 'd' : '.',
    @@ -584,9 +672,12 @@ print_lat_fmt(struct seq_file *m, struct
    abs_usecs = cycles_to_usecs(entry->t - iter->tr->time_start);

    if (verbose) {
    + char *comm;
    +
    + comm = trace_find_cmdline(entry->pid);
    seq_printf(m, "%16s %5d %d %d %08x %08x [%08lx]"
    " %ld.%03ldms (+%ld.%03ldms): ",
    - entry->comm,
    + comm,
    entry->pid, cpu, entry->flags,
    entry->preempt_count, trace_idx,
    cycles_to_usecs(entry->t),
    @@ -623,6 +714,9 @@ static void notrace print_trace_fmt(stru
    unsigned long secs;
    int sym_only = !!(trace_flags & TRACE_ITER_SYM_ONLY);
    unsigned long long t;
    + char *comm;
    +
    + comm = trace_find_cmdline(iter->ent->pid);

    t = cycles_to_usecs(iter->ent->t);
    usec_rem = do_div(t, 1000000ULL);
    @@ -630,7 +724,7 @@ static void notrace print_trace_fmt(stru

    seq_printf(m, "[%5lu.%06lu] ", secs, usec_rem);
    seq_printf(m, "CPU %d: ", iter->cpu);
    - seq_printf(m, "%s:%d ", iter->ent->comm,
    + seq_printf(m, "%s:%d ", comm,
    iter->ent->pid);
    switch (iter->ent->type) {
    case TRACE_FN:
    @@ -1164,6 +1258,8 @@ __init static int tracer_alloc_buffers(v

    tracer_init_debugfs();

    + trace_init_cmdlines();
    +
    return 0;

    free_buffers:
    Index: linux-mcount.git/lib/tracing/tracer.h
    ===================================================================
    --- linux-mcount.git.orig/lib/tracing/tracer.h 2008-01-23 10:27:31.000000000 -0500
    +++ linux-mcount.git/lib/tracing/tracer.h 2008-01-23 10:27:39.000000000 -0500
    @@ -25,7 +25,6 @@ struct tracing_entry {
    char preempt_count; /* assumes PREEMPT_MASK is 8 bits or less */
    int pid;
    cycle_t t;
    - char comm[TASK_COMM_LEN];
    union {
    struct tracing_function fn;
    struct tracing_sched_switch ctx;
    @@ -98,13 +97,16 @@ void tracing_sched_switch_trace(struct t
    struct task_struct *prev,
    struct task_struct *next,
    unsigned long flags);
    -
    +void tracing_record_cmdline(struct task_struct *tsk);

    void tracing_start_function_trace(void);
    void tracing_stop_function_trace(void);
    int register_trace(struct trace_types_struct *type);
    void unregister_trace(struct trace_types_struct *type);

    +extern atomic_t trace_record_cmdline;
    +extern atomic_t trace_record_cmdline_disabled;
    +
    static inline notrace cycle_t now(void)
    {
    return get_monotonic_cycles();
    --


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