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Date: Thu, 08 May 2014 15:14:04 -0700 From: Jason Low <jason.low2@...com> To: Ingo Molnar <mingo@...nel.org>, jason.low2@...com Cc: peterz@...radead.org, linux-kernel@...r.kernel.org, daniel.lezcano@...aro.org, alex.shi@...aro.org, preeti@...ux.vnet.ibm.com, efault@....de, vincent.guittot@...aro.org, morten.rasmussen@....com, aswin@...com Subject: Re: [PATCH 2/2] sched: Fix next_balance logic in rebalance_domains() and idle_balance() On Thu, 2014-05-08 at 19:38 +0200, Ingo Molnar wrote: > * Jason Low <jason.low2@...com> wrote: > > > On Mon, 2014-04-28 at 15:45 -0700, Jason Low wrote: > > > Currently, in idle_balance(), we update rq->next_balance when we pull_tasks. > > > However, it is also important to update this in the !pulled_tasks case too. > > > > > > When the CPU is "busy" (the CPU isn't idle), rq->next_balance gets computed > > > using sd->busy_factor (so we increase the balance interval when the CPU is > > > busy). However, when the CPU goes idle, rq->next_balance could still be set > > > to a large value that was computed with the sd->busy_factor. > > > > > > Thus, we need to also update rq->next_balance in idle_balance() in the cases > > > where !pulled_tasks too, so that rq->next_balance gets updated without taking > > > the busy_factor into account when the CPU is about to go idle. > > > > > > This patch makes rq->next_balance get updated independently of whether or > > > not we pulled_task. Also, we add logic to ensure that we always traverse > > > at least 1 of the sched domains to get a proper next_balance value for > > > updating rq->next_balance. > > > > > > Additionally, since load_balance() modifies the sd->balance_interval, we > > > need to re-obtain the sched domain's interval after the call to > > > load_balance() in rebalance_domains() before we update rq->next_balance. > > > > > > This patch adds and uses 2 new helper functions, update_next_balance() and > > > get_sd_balance_interval() to update next_balance and obtain the sched > > > domain's balance_interval. > > > > > > Hi Peter, > > > > I noticed that patch 1 is in tip, but not this patch 2. I was wondering > > what the current status with this [PATCH 2/2] is at the moment. > > It was crashing the bootup with the attached config, it gave the splat > attached below. (ignore the line duplication, it's a serial logging > artifact.) Hi Ingo, Peter, Were there NULL domains on the test system? If so, I think we can address the problem by doing update_next_balance() only if the below rcu_dereference_check_sched_domain() returns a non-null domain. @@ -6665,8 +6692,14 @@ static int idle_balance(struct rq *this_rq) > */ > this_rq->idle_stamp = rq_clock(this_rq); > > - if (this_rq->avg_idle < sysctl_sched_migration_cost) > + if (this_rq->avg_idle < sysctl_sched_migration_cost) { > + rcu_read_lock(); > + sd = rcu_dereference_check_sched_domain(this_rq->sd); > + update_next_balance(sd, 0, &next_balance); > + rcu_read_unlock(); > + > goto out; > + } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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