Re: [PATCH 5/5] sched/fair: Skip LLC nohz logic for asymmetric systems

2019-02-07 Thread Valentin Schneider
On 07/02/2019 09:56, Peter Zijlstra wrote: [...] >> I'm afraid I don't follow - we don't lose a balance opportunity with the >> below change (compared to the original patch), do we? > > What if each big/little cluster would have multiple cache domains? Would > we not want to spread the cache

Re: [PATCH 5/5] sched/fair: Skip LLC nohz logic for asymmetric systems

2019-02-07 Thread Peter Zijlstra
On Wed, Feb 06, 2019 at 05:26:06PM +, Valentin Schneider wrote: > Hi, > > On 06/02/2019 16:14, Peter Zijlstra wrote: > [...] > >> @@ -9545,6 +9545,17 @@ static void nohz_balancer_kick(struct rq *rq) > >>} > >> > >>rcu_read_lock(); > >> + > >> + if

Re: [PATCH 5/5] sched/fair: Skip LLC nohz logic for asymmetric systems

2019-02-06 Thread Valentin Schneider
Hi, On 06/02/2019 16:14, Peter Zijlstra wrote: [...] >> @@ -9545,6 +9545,17 @@ static void nohz_balancer_kick(struct rq *rq) >> } >> >> rcu_read_lock(); >> + >> +if (static_branch_unlikely(_asym_cpucapacity)) >> +/* >> + * For asymmetric systems, we do not

Re: [PATCH 5/5] sched/fair: Skip LLC nohz logic for asymmetric systems

2019-02-06 Thread Peter Zijlstra
On Thu, Jan 17, 2019 at 03:34:11PM +, Valentin Schneider wrote: > The LLC nohz condition will become true as soon as >=2 CPUs in a > single LLC domain are busy. On big.LITTLE systems, this translates to > two or more CPUs of a "cluster" (big or LITTLE) being busy. > > Issuing a nohz kick in

[PATCH 5/5] sched/fair: Skip LLC nohz logic for asymmetric systems

2019-01-17 Thread Valentin Schneider
The LLC nohz condition will become true as soon as >=2 CPUs in a single LLC domain are busy. On big.LITTLE systems, this translates to two or more CPUs of a "cluster" (big or LITTLE) being busy. Issuing a nohz kick in these conditions isn't desired for asymmetric systems, as if the busy CPUs can