On Tue, 2007-11-13 at 20:14 -0500, Chuck Ebbert wrote: > https://bugzilla.redhat.com/show_bug.cgi?id=340161
While I see the user has a divide by zero, I'm not understanding it.
> The problem code has been removed in 2.6.24. The below patch disables
> SCHED_FEAT_PRECISE_CPU_LOAD which causes the offending code to be skipped
> but does not prevent the user from enabling it.
>
> The divide-by-zero is here in kernel/sched.c:
>
> static void update_cpu_load(struct rq *this_rq)
> {
> u64 fair_delta64, exec_delta64, idle_delta64, sample_interval64, tmp64;
> unsigned long total_load = this_rq->ls.load.weight;
> unsigned long this_load = total_load;
> struct load_stat *ls = &this_rq->ls;
> int i, scale;
>
> this_rq->nr_load_updates++;
> if (unlikely(!(sysctl_sched_features & SCHED_FEAT_PRECISE_CPU_LOAD)))
> goto do_avg;
>
> /* Update delta_fair/delta_exec fields first */
> update_curr_load(this_rq);
>
> fair_delta64 = ls->delta_fair + 1;
Shouldn't that +1 avoid fair_delta64 from being 0?
> ls->delta_fair = 0;
>
> exec_delta64 = ls->delta_exec + 1;
> ls->delta_exec = 0;
>
> sample_interval64 = this_rq->clock - ls->load_update_last;
> ls->load_update_last = this_rq->clock;
>
> if ((s64)sample_interval64 < (s64)TICK_NSEC)
> sample_interval64 = TICK_NSEC;
This avoids sample_interval64 from being 0.
> if (exec_delta64 > sample_interval64)
> exec_delta64 = sample_interval64;
>
> idle_delta64 = sample_interval64 - exec_delta64;
>
> ======> tmp64 = div64_64(SCHED_LOAD_SCALE * exec_delta64, fair_delta64);
> tmp64 = div64_64(tmp64 * exec_delta64, sample_interval64);
>
> this_load = (unsigned long)tmp64;
>
> do_avg:
>
> /* Update our load: */
> for (i = 0, scale = 1; i < CPU_LOAD_IDX_MAX; i++, scale += scale) {
> unsigned long old_load, new_load;
>
> /* scale is effectively 1 << i now, and >> i divides by scale */
>
> old_load = this_rq->cpu_load[i];
> new_load = this_load;
>
> this_rq->cpu_load[i] = (old_load*(scale-1) + new_load) >> i;
> }
> }
>
As for the patch, better to just rip out the entire feature..
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