Messages in this thread | | | Date | Mon, 28 Apr 2008 16:27:36 +0800 | From | Miao Xie <> | Subject | Re: [PATCH] sched: fair-group: fix a Div0 error of the fair group scheduler |
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on 2008-4-28 13:45 Peter Zijlstra wrote: > On Mon, 2008-04-28 at 12:54 +0800, Miao Xie wrote: >> When I echoed 0 into the "cpu.shares" file, a Div0 error occured. >> >> We found it is caused by the following calling. >> >> sched_group_set_shares(tg, shares) >> set_se_shares(tg->se[i], shares/nr_cpu_ids) >> __set_se_shares(se, shares) >> div64_64((1ULL<<32), shares) >> >> When the echoed value was less than the number of processores, the result of the >> sentence "shares/nr_cpu_ids" was 0, and then the system called div64() to divide >> the result, the Div0 error occured. >> >> It is unnecessary that the shares value is divided by nr_cpu_ids, I think. >> Because in the function __update_group_shares_cpu() and init_tg_cfs_entry(), >> the shares value isn't divided by nr_cpu_ids when setting shares of the sched >> entity. >> >> This patch fixes this bug. And echoing ULONG_MAX value into cpu.shares also >> causes Div0 error, so we set a macro MAX_SHARES to limit the max value of >> shares. > > how about: > > diff --git a/kernel/sched.c b/kernel/sched.c > index 740fb40..b68127a 100644 > --- a/kernel/sched.c > +++ b/kernel/sched.c > @@ -8025,7 +8025,7 @@ static void init_tg_cfs_entry(struct task_group *tg, struct cfs_rq *cfs_rq, > > se->my_q = cfs_rq; > se->load.weight = tg->shares; > - se->load.inv_weight = div64_64(1ULL<<32, se->load.weight); > + se->load.inv_weight = 0; > se->parent = parent; > } > #endif > @@ -8692,7 +8692,7 @@ static void __set_se_shares(struct sched_entity *se, unsigned long shares) > dequeue_entity(cfs_rq, se, 0); > > se->load.weight = shares; > - se->load.inv_weight = div64_64((1ULL<<32), shares); > + se->load.inv_weight = 0; > > if (on_rq) > enqueue_entity(cfs_rq, se, 0); >
I'm sorry, I didn't explained clearly.Though echoing ULONG_MAX value into cpu.shares causes Div0 error, this error was not caused by the above code. It is caused by the following code.
calc_delta_mine() ->lw->inv_weight = (WMULT_CONST-lw->weight/2) / (lw->weight+1);
And besides, the Div0 error caused by echoing ULONG_MAX occured on the UP system or on SMP system with only one cpu.
So this patch fixes the bug caused by echoing a number which was less than the number of processores into the "cpu.shares" file, but doesn't fix the bug caused by echoing ULONG_MAX.
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