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    Subject[PATCH v2 5/5] sched, timer: Use the atomic task_cputime in thread_group_cputimer
    Date
    Recent optimizations were made to thread_group_cputimer to improve its
    scalability by keeping track of cputime stats without a lock. However,
    the values were open coded to the structure, causing them to be at
    a different abstraction level from the regular task_cputime structure.
    Furthermore, any subsequent similar optimizations would not be able to
    share the new code, since they are specific to thread_group_cputimer.

    This patch adds the new task_cputime_atomic data structure (introduced in
    the previous patch in the series) to thread_group_cputimer for keeping
    track of the cputime atomically, which also helps generalize the code.

    Suggested-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Jason Low <jason.low2@hp.com>
    ---
    include/linux/init_task.h | 6 ++----
    include/linux/sched.h | 4 +---
    kernel/sched/stats.h | 6 +++---
    kernel/time/posix-cpu-timers.c | 26 +++++++++++++-------------
    4 files changed, 19 insertions(+), 23 deletions(-)

    diff --git a/include/linux/init_task.h b/include/linux/init_task.h
    index 7b9d8b5..bb9b075 100644
    --- a/include/linux/init_task.h
    +++ b/include/linux/init_task.h
    @@ -50,10 +50,8 @@ extern struct fs_struct init_fs;
    .cpu_timers = INIT_CPU_TIMERS(sig.cpu_timers), \
    .rlim = INIT_RLIMITS, \
    .cputimer = { \
    - .utime = ATOMIC64_INIT(0), \
    - .stime = ATOMIC64_INIT(0), \
    - .sum_exec_runtime = ATOMIC64_INIT(0), \
    - .running = 0 \
    + .cputime_atomic = INIT_CPUTIME_ATOMIC, \
    + .running = 0, \
    }, \
    .cred_guard_mutex = \
    __MUTEX_INITIALIZER(sig.cred_guard_mutex), \
    diff --git a/include/linux/sched.h b/include/linux/sched.h
    index 7092192..80ce921c 100644
    --- a/include/linux/sched.h
    +++ b/include/linux/sched.h
    @@ -618,9 +618,7 @@ struct task_cputime_atomic {
    * used for thread group CPU timer calculations.
    */
    struct thread_group_cputimer {
    - atomic64_t utime;
    - atomic64_t stime;
    - atomic64_t sum_exec_runtime;
    + struct task_cputime_atomic cputime_atomic;
    int running;
    };

    diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
    index c6d1c7d..077ebbd 100644
    --- a/kernel/sched/stats.h
    +++ b/kernel/sched/stats.h
    @@ -216,7 +216,7 @@ static inline void account_group_user_time(struct task_struct *tsk,
    if (!cputimer_running(tsk))
    return;

    - atomic64_add(cputime, &cputimer->utime);
    + atomic64_add(cputime, &cputimer->cputime_atomic.utime);
    }

    /**
    @@ -237,7 +237,7 @@ static inline void account_group_system_time(struct task_struct *tsk,
    if (!cputimer_running(tsk))
    return;

    - atomic64_add(cputime, &cputimer->stime);
    + atomic64_add(cputime, &cputimer->cputime_atomic.stime);
    }

    /**
    @@ -258,5 +258,5 @@ static inline void account_group_exec_runtime(struct task_struct *tsk,
    if (!cputimer_running(tsk))
    return;

    - atomic64_add(ns, &cputimer->sum_exec_runtime);
    + atomic64_add(ns, &cputimer->cputime_atomic.sum_exec_runtime);
    }
    diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
    index d857306..892e3da 100644
    --- a/kernel/time/posix-cpu-timers.c
    +++ b/kernel/time/posix-cpu-timers.c
    @@ -211,20 +211,20 @@ retry:
    }
    }

    -static void update_gt_cputime(struct thread_group_cputimer *cputimer, struct task_cputime *sum)
    +static void update_gt_cputime(struct task_cputime_atomic *cputime_atomic, struct task_cputime *sum)
    {
    - __update_gt_cputime(&cputimer->utime, sum->utime);
    - __update_gt_cputime(&cputimer->stime, sum->stime);
    - __update_gt_cputime(&cputimer->sum_exec_runtime, sum->sum_exec_runtime);
    + __update_gt_cputime(&cputime_atomic->utime, sum->utime);
    + __update_gt_cputime(&cputime_atomic->stime, sum->stime);
    + __update_gt_cputime(&cputime_atomic->sum_exec_runtime, sum->sum_exec_runtime);
    }

    -/* Sample thread_group_cputimer values in "cputimer", store results in "times". */
    -static inline void sample_group_cputimer(struct task_cputime *times,
    - struct thread_group_cputimer *cputimer)
    +/* Sample task_cputime_atomic values in "atomic_timers", store results in "times". */
    +static inline void sample_cputime_atomic(struct task_cputime *times,
    + struct task_cputime_atomic *atomic_times)
    {
    - times->utime = atomic64_read(&cputimer->utime);
    - times->stime = atomic64_read(&cputimer->stime);
    - times->sum_exec_runtime = atomic64_read(&cputimer->sum_exec_runtime);
    + times->utime = atomic64_read(&atomic_times->utime);
    + times->stime = atomic64_read(&atomic_times->stime);
    + times->sum_exec_runtime = atomic64_read(&atomic_times->sum_exec_runtime);
    }

    void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
    @@ -240,7 +240,7 @@ void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
    * to synchronize the timer to the clock every time we start it.
    */
    thread_group_cputime(tsk, &sum);
    - update_gt_cputime(cputimer, &sum);
    + update_gt_cputime(&cputimer->cputime_atomic, &sum);

    /*
    * We're setting cputimer->running without a lock. Ensure
    @@ -251,7 +251,7 @@ void thread_group_cputimer(struct task_struct *tsk, struct task_cputime *times)
    */
    WRITE_ONCE(cputimer->running, 1);
    }
    - sample_group_cputimer(times, cputimer);
    + sample_cputime_atomic(times, &cputimer->cputime_atomic);
    }

    /*
    @@ -1137,7 +1137,7 @@ static inline int fastpath_timer_check(struct task_struct *tsk)
    if (READ_ONCE(sig->cputimer.running)) {
    struct task_cputime group_sample;

    - sample_group_cputimer(&group_sample, &sig->cputimer);
    + sample_cputime_atomic(&group_sample, &sig->cputimer.cputime_atomic);

    if (task_cputime_expired(&group_sample, &sig->cputime_expires))
    return 1;
    --
    1.7.2.5


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