Messages in this thread | | | Subject | Re: High CPU load when machine is idle (related to PROBLEM: Unusually high load average when idle in 2.6.35, 2.6.35.1 and later) | From | Peter Zijlstra <> | Date | Thu, 21 Oct 2010 14:09:59 +0200 |
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On Wed, 2010-10-20 at 19:26 +0200, Peter Zijlstra wrote:
> -static void calc_load_account_idle(struct rq *this_rq) > +void calc_load_account_idle(void) > { > + struct rq *this_rq = this_rq(); > long delta; > > delta = calc_load_fold_active(this_rq); > + this_rq->calc_load_inactive = delta; > + this_rq->calc_load_seq = atomic_read(&calc_load_seq); > + > if (delta) > atomic_long_add(delta, &calc_load_tasks_idle); > } > > +void calc_load_account_nonidle(void) > +{ > + struct rq *this_rq = this_rq(); > + > + if (atomic_read(&calc_load_seq) == this_rq->calc_load_seq) { > + atomic_long_sub(this_rq->calc_load_inactive, &calc_load_tasks_idle); > + /* > + * Undo the _fold_active() from _account_idle(). This > + * avoids us loosing active tasks and creating a negative > + * bias > + */ > + this_rq->calc_load_active -= this_rq->calc_load_inactive; > + } > +}
Ok, so while trying to write a changelog on this patch I got myself terribly confused again..
calc_load_active_fold() is a relative operation and simply gives delta values since the last time it got called. That means that the sum of multiple invocations in a given time interval should be identical to a single invocation.
Therefore, the going idle multiple times during LOAD_FREQ hypothesis doesn't really make sense.
Even if it became idle but wasn't idle at the LOAD_FREQ turn-over it shouldn't matter, since the calc_load_account_active() call will simply fold the remaining delta with the accrued idle delta and the total should all match up once we fold into the global calc_load_tasks.
So afaict its should all have worked and this patch is a big NOP,. except it isn't..
Damn I hate this bug.. ;-) Anybody?
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