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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