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    Subject[PATCH 17/18] sched: Add tracepoints related to NUMA task migration
    Date
    This patch adds three tracepoints
    o trace_sched_move_numa when a task is moved to a node
    o trace_sched_swap_numa when a task is swapped with another task
    o trace_sched_stick_numa when a numa-related migration fails

    The tracepoints allow the NUMA scheduler activity to be monitored and the
    following high-level metrics can be calculated

    o NUMA migrated stuck nr trace_sched_stick_numa
    o NUMA migrated idle nr trace_sched_move_numa
    o NUMA migrated swapped nr trace_sched_swap_numa
    o NUMA local swapped trace_sched_swap_numa src_nid == dst_nid (should never happen)
    o NUMA remote swapped trace_sched_swap_numa src_nid != dst_nid (should == NUMA migrated swapped)
    o NUMA group swapped trace_sched_swap_numa src_ngid == dst_ngid
    Maybe a small number of these are acceptable
    but a high number would be a major surprise.
    It would be even worse if bounces are frequent.
    o NUMA avg task migs. Average number of migrations for tasks
    o NUMA stddev task mig Self-explanatory
    o NUMA max task migs. Maximum number of migrations for a single task

    In general the intent of the tracepoints is to help diagnose problems
    where automatic NUMA balancing appears to be doing an excessive amount of
    useless work.

    Signed-off-by: Mel Gorman <mgorman@suse.de>
    Reviewed-by: Rik van Riel <riel@redhat.com>
    ---
    include/trace/events/sched.h | 87 ++++++++++++++++++++++++++++++++++++++++++++
    kernel/sched/core.c | 2 +
    kernel/sched/fair.c | 6 ++-
    3 files changed, 93 insertions(+), 2 deletions(-)

    diff --git a/include/trace/events/sched.h b/include/trace/events/sched.h
    index 04c3084..67e1bbf 100644
    --- a/include/trace/events/sched.h
    +++ b/include/trace/events/sched.h
    @@ -443,6 +443,93 @@ TRACE_EVENT(sched_process_hang,
    );
    #endif /* CONFIG_DETECT_HUNG_TASK */

    +DECLARE_EVENT_CLASS(sched_move_task_template,
    +
    + TP_PROTO(struct task_struct *tsk, int src_cpu, int dst_cpu),
    +
    + TP_ARGS(tsk, src_cpu, dst_cpu),
    +
    + TP_STRUCT__entry(
    + __field( pid_t, pid )
    + __field( pid_t, tgid )
    + __field( pid_t, ngid )
    + __field( int, src_cpu )
    + __field( int, src_nid )
    + __field( int, dst_cpu )
    + __field( int, dst_nid )
    + ),
    +
    + TP_fast_assign(
    + __entry->pid = task_pid_nr(tsk);
    + __entry->tgid = task_tgid_nr(tsk);
    + __entry->ngid = task_numa_group_id(tsk);
    + __entry->src_cpu = src_cpu;
    + __entry->src_nid = cpu_to_node(src_cpu);
    + __entry->dst_cpu = dst_cpu;
    + __entry->dst_nid = cpu_to_node(dst_cpu);
    + ),
    +
    + TP_printk("pid=%d tgid=%d ngid=%d src_cpu=%d src_nid=%d dst_cpu=%d dst_nid=%d",
    + __entry->pid, __entry->tgid, __entry->ngid,
    + __entry->src_cpu, __entry->src_nid,
    + __entry->dst_cpu, __entry->dst_nid)
    +);
    +
    +/*
    + * Tracks migration of tasks from one runqueue to another. Can be used to
    + * detect if automatic NUMA balancing is bouncing between nodes
    + */
    +DEFINE_EVENT(sched_move_task_template, sched_move_numa,
    + TP_PROTO(struct task_struct *tsk, int src_cpu, int dst_cpu),
    +
    + TP_ARGS(tsk, src_cpu, dst_cpu)
    +);
    +
    +DEFINE_EVENT(sched_move_task_template, sched_stick_numa,
    + TP_PROTO(struct task_struct *tsk, int src_cpu, int dst_cpu),
    +
    + TP_ARGS(tsk, src_cpu, dst_cpu)
    +);
    +
    +TRACE_EVENT(sched_swap_numa,
    +
    + TP_PROTO(struct task_struct *src_tsk, int src_cpu,
    + struct task_struct *dst_tsk, int dst_cpu),
    +
    + TP_ARGS(src_tsk, src_cpu, dst_tsk, dst_cpu),
    +
    + TP_STRUCT__entry(
    + __field( pid_t, src_pid )
    + __field( pid_t, src_tgid )
    + __field( pid_t, src_ngid )
    + __field( int, src_cpu )
    + __field( int, src_nid )
    + __field( pid_t, dst_pid )
    + __field( pid_t, dst_tgid )
    + __field( pid_t, dst_ngid )
    + __field( int, dst_cpu )
    + __field( int, dst_nid )
    + ),
    +
    + TP_fast_assign(
    + __entry->src_pid = task_pid_nr(src_tsk);
    + __entry->src_tgid = task_tgid_nr(src_tsk);
    + __entry->src_ngid = task_numa_group_id(src_tsk);
    + __entry->src_cpu = src_cpu;
    + __entry->src_nid = cpu_to_node(src_cpu);
    + __entry->dst_pid = task_pid_nr(dst_tsk);
    + __entry->dst_tgid = task_tgid_nr(dst_tsk);
    + __entry->dst_ngid = task_numa_group_id(dst_tsk);
    + __entry->dst_cpu = dst_cpu;
    + __entry->dst_nid = cpu_to_node(dst_cpu);
    + ),
    +
    + TP_printk("src_pid=%d src_tgid=%d src_ngid=%d src_cpu=%d src_nid=%d dst_pid=%d dst_tgid=%d dst_ngid=%d dst_cpu=%d dst_nid=%d",
    + __entry->src_pid, __entry->src_tgid, __entry->src_ngid,
    + __entry->src_cpu, __entry->src_nid,
    + __entry->dst_pid, __entry->dst_tgid, __entry->dst_ngid,
    + __entry->dst_cpu, __entry->dst_nid)
    +);
    #endif /* _TRACE_SCHED_H */

    /* This part must be outside protection */
    diff --git a/kernel/sched/core.c b/kernel/sched/core.c
    index e85cda2..e485d2b 100644
    --- a/kernel/sched/core.c
    +++ b/kernel/sched/core.c
    @@ -1108,6 +1108,7 @@ int migrate_swap(struct task_struct *cur, struct task_struct *p)
    if (!cpumask_test_cpu(arg.src_cpu, tsk_cpus_allowed(arg.dst_task)))
    goto out;

    + trace_sched_swap_numa(cur, arg.src_cpu, p, arg.dst_cpu);
    ret = stop_two_cpus(arg.dst_cpu, arg.src_cpu, migrate_swap_stop, &arg);

    out:
    @@ -4090,6 +4091,7 @@ int migrate_task_to(struct task_struct *p, int target_cpu)

    /* TODO: This is not properly updating schedstats */

    + trace_sched_move_numa(p, curr_cpu, target_cpu);
    return stop_one_cpu(curr_cpu, migration_cpu_stop, &arg);
    }

    diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
    index 18bf84e..26fe588 100644
    --- a/kernel/sched/fair.c
    +++ b/kernel/sched/fair.c
    @@ -1272,11 +1272,13 @@ static int task_numa_migrate(struct task_struct *p)
    p->numa_scan_period = task_scan_min(p);

    if (env.best_task == NULL) {
    - int ret = migrate_task_to(p, env.best_cpu);
    + if ((ret = migrate_task_to(p, env.best_cpu)) != 0)
    + trace_sched_stick_numa(p, env.src_cpu, env.best_cpu);
    return ret;
    }

    - ret = migrate_swap(p, env.best_task);
    + if ((ret = migrate_swap(p, env.best_task)) != 0);
    + trace_sched_stick_numa(p, env.src_cpu, task_cpu(env.best_task));
    put_task_struct(env.best_task);
    return ret;
    }
    --
    1.8.4


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