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    Subject[PATCH 12/24] sched: Update rq clock on nohz CPU before migrating tasks
    Date
    Because the sched_class::put_prev_task() callback of rt and fair
    classes are referring to the rq clock to update their runtime
    statistics. A CPU running in tickless mode may carry a stale value.
    We need to update it there.

    Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
    Cc: Alessio Igor Bogani <abogani@kernel.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Avi Kivity <avi@redhat.com>
    Cc: Chris Metcalf <cmetcalf@tilera.com>
    Cc: Christoph Lameter <cl@linux.com>
    Cc: Geoff Levand <geoff@infradead.org>
    Cc: Gilad Ben Yossef <gilad@benyossef.com>
    Cc: Hakan Akkan <hakanakkan@gmail.com>
    Cc: Ingo Molnar <mingo@kernel.org>
    Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    ---
    kernel/sched/core.c | 6 ++++++
    kernel/sched/sched.h | 7 +++++++
    2 files changed, 13 insertions(+), 0 deletions(-)

    diff --git a/kernel/sched/core.c b/kernel/sched/core.c
    index 02bd005..5d9060a 100644
    --- a/kernel/sched/core.c
    +++ b/kernel/sched/core.c
    @@ -4832,6 +4832,12 @@ static void migrate_tasks(unsigned int dead_cpu)
    */
    rq->stop = NULL;

    + /*
    + * ->put_prev_task() need to have an up-to-date value
    + * of rq->clock[_task]
    + */
    + update_nohz_rq_clock(rq);
    +
    for ( ; ; ) {
    /*
    * There's this thread running, bail when that's the only
    diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
    index 5eca173..db3d4df 100644
    --- a/kernel/sched/sched.h
    +++ b/kernel/sched/sched.h
    @@ -3,6 +3,7 @@
    #include <linux/mutex.h>
    #include <linux/spinlock.h>
    #include <linux/stop_machine.h>
    +#include <linux/tick.h>

    #include "cpupri.h"

    @@ -951,6 +952,12 @@ static inline void dec_nr_running(struct rq *rq)

    extern void update_rq_clock(struct rq *rq);

    +static inline void update_nohz_rq_clock(struct rq *rq)
    +{
    + if (tick_nohz_full_cpu(cpu_of(rq)))
    + update_rq_clock(rq);
    +}
    +
    extern void activate_task(struct rq *rq, struct task_struct *p, int flags);
    extern void deactivate_task(struct rq *rq, struct task_struct *p, int flags);

    --
    1.7.5.4


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