[PATCH 1/1] sched: defer idle accounting till after load update period
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From: Chase Douglas on 21 Mar 2010 18:50 There's a period of 10 ticks where calc_load_tasks is updated by all the cpus for the load avg. Usually all the cpus do this during the first tick. If any cpus go idle, calc_load_tasks is decremented accordingly. However, if they wake up calc_load_tasks is not incremented. Thus, if cpus go idle during the 10 tick period, calc_load_tasks may be decremented to a non-representative value. This issue can lead to systems having a load avg of exactly 0, even though the real load avg could theoretically be up to NR_CPUS. This change defers calc_load_tasks accounting after each cpu updates the count until after the 10 tick period. BugLink: http://bugs.launchpad.net/bugs/513848 Signed-off-by: Chase Douglas <chase.douglas(a)canonical.com> --- kernel/sched.c | 16 ++++++++++++++-- 1 files changed, 14 insertions(+), 2 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index 9ab3cd7..c0aedac 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -3064,7 +3064,8 @@ void calc_global_load(void) */ static void calc_load_account_active(struct rq *this_rq) { - long nr_active, delta; + static atomic_long_t deferred; + long nr_active, delta, deferred_delta; nr_active = this_rq->nr_running; nr_active += (long) this_rq->nr_uninterruptible; @@ -3072,6 +3073,17 @@ static void calc_load_account_active(struct rq *this_rq) if (nr_active != this_rq->calc_load_active) { delta = nr_active - this_rq->calc_load_active; this_rq->calc_load_active = nr_active; + + /* Need to defer idle accounting during load update period: */ + if (unlikely(time_before(jiffies, this_rq->calc_load_update) && + time_after_eq(jiffies, calc_load_update))) { + atomic_long_add(delta, &deferred); + return; + } + + deferred_delta = atomic_long_xchg(&deferred, 0); + delta += deferred_delta; + atomic_long_add(delta, &calc_load_tasks); } } @@ -3106,8 +3118,8 @@ static void update_cpu_load(struct rq *this_rq) } if (time_after_eq(jiffies, this_rq->calc_load_update)) { - this_rq->calc_load_update += LOAD_FREQ; calc_load_account_active(this_rq); + this_rq->calc_load_update += LOAD_FREQ; } } -- 1.6.3.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |