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    Subject[PATCH 15/23 -v8] 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 | 5 +
    lib/tracing/tracer.c | 108 ++++++++++++++++++++++++++++++++++++---
    lib/tracing/tracer.h | 3 -
    5 files changed, 111 insertions(+), 8 deletions(-)

    Index: linux-mcount.git/lib/tracing/Kconfig
    ===================================================================
    --- linux-mcount.git.orig/lib/tracing/Kconfig 2008-01-30 15:32:33.000000000 -0500
    +++ linux-mcount.git/lib/tracing/Kconfig 2008-01-30 15:33:38.000000000 -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 2008-01-30 15:18:18.000000000 -0500
    +++ linux-mcount.git/lib/tracing/trace_function.c 2008-01-30 15:33:38.000000000 -0500
    @@ -29,10 +29,12 @@ static notrace void start_function_trace
    {
    function_reset(tr);
    tracing_start_function_trace();
    + tracing_start_sched_switch();
    }

    static notrace void stop_function_trace(struct tracing_trace *tr)
    {
    + tracing_stop_sched_switch();
    tracing_stop_function_trace();
    }

    Index: linux-mcount.git/lib/tracing/trace_sched_switch.c
    ===================================================================
    --- linux-mcount.git.orig/lib/tracing/trace_sched_switch.c 2008-01-30 15:32:34.000000000 -0500
    +++ linux-mcount.git/lib/tracing/trace_sched_switch.c 2008-01-30 15:33:38.000000000 -0500
    @@ -33,6 +33,11 @@ static notrace void sched_switch_callbac
    va_list ap;
    int cpu;

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

    Index: linux-mcount.git/lib/tracing/tracer.c
    ===================================================================
    --- linux-mcount.git.orig/lib/tracing/tracer.c 2008-01-30 15:32:34.000000000 -0500
    +++ linux-mcount.git/lib/tracing/tracer.c 2008-01-30 15:33:38.000000000 -0500
    @@ -172,6 +172,87 @@ 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_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)
    @@ -213,7 +294,6 @@ 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,
    @@ -369,6 +449,8 @@ 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);
    @@ -396,6 +478,8 @@ 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);
    @@ -524,8 +608,11 @@ 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' : '.',
    @@ -577,6 +664,7 @@ print_lat_fmt(struct seq_file *m, struct
    struct tracing_entry *next_entry = find_next_entry(iter, NULL);
    unsigned long abs_usecs;
    unsigned long rel_usecs;
    + char *comm;
    int sym_only = !!(trace_flags & TRACE_ITER_SYM_ONLY);
    int verbose = !!(trace_flags & TRACE_ITER_VERBOSE);
    int S;
    @@ -587,9 +675,10 @@ print_lat_fmt(struct seq_file *m, struct
    abs_usecs = cycles_to_usecs(entry->t - iter->tr->time_start);

    if (verbose) {
    + 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),
    @@ -609,12 +698,14 @@ print_lat_fmt(struct seq_file *m, struct
    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",
    + comm = trace_find_cmdline(entry->ctx.next_pid);
    + seq_printf(m, " %d:%d:%c --> %d:%d %s\n",
    entry->ctx.prev_pid,
    entry->ctx.prev_prio,
    S,
    entry->ctx.next_pid,
    - entry->ctx.next_prio);
    + entry->ctx.next_prio,
    + comm);
    break;
    }
    }
    @@ -627,15 +718,18 @@ 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;
    int S;

    + comm = trace_find_cmdline(iter->ent->pid);
    +
    t = cycles_to_usecs(entry->t);
    usec_rem = do_div(t, 1000000ULL);
    secs = (unsigned long)t;

    seq_printf(m, "[%5lu.%06lu] ", secs, usec_rem);
    seq_printf(m, "CPU %d: ", iter->cpu);
    - seq_printf(m, "%s:%d ", entry->comm,
    + seq_printf(m, "%s:%d ", comm,
    entry->pid);
    switch (entry->type) {
    case TRACE_FN:
    @@ -1189,6 +1283,8 @@ __init static int tracer_alloc_buffers(v

    tracer_init_debugfs();

    + trace_init_cmdlines();
    +
    register_trace(&disable_trace);

    return 0;
    Index: linux-mcount.git/lib/tracing/tracer.h
    ===================================================================
    --- linux-mcount.git.orig/lib/tracing/tracer.h 2008-01-30 15:32:34.000000000 -0500
    +++ linux-mcount.git/lib/tracing/tracer.h 2008-01-30 15:33:38.000000000 -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;
    @@ -98,7 +97,7 @@ 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);
    --


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