From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758064Ab3J2DeO (ORCPT ); Mon, 28 Oct 2013 23:34:14 -0400 Received: from e23smtp01.au.ibm.com ([202.81.31.143]:42768 "EHLO e23smtp01.au.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757559Ab3J2DeN (ORCPT ); Mon, 28 Oct 2013 23:34:13 -0400 Message-ID: <526F2BEC.3040207@linux.vnet.ibm.com> Date: Tue, 29 Oct 2013 09:00:52 +0530 From: Preeti U Murthy User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0 MIME-Version: 1.0 To: Peter Zijlstra CC: Vincent Guittot , Ingo Molnar , Vaidyanathan Srinivasan , Mike Galbraith , Paul Turner , Michael Neuling , Benjamin Herrenschmidt , linux-kernel , Anton Blanchard , linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH 1/3] sched: Fix nohz_kick_needed to consider the nr_busy of the parent domain's group References: <20131021114002.13291.31478.stgit@drishya> <20131021114442.13291.99344.stgit@drishya> <20131022221138.GJ2490@laptop.programming.kicks-ass.net> <52679BD6.6090507@linux.vnet.ibm.com> <5268D54A.9060604@linux.vnet.ibm.com> <20131028135043.GP19466@laptop.lan> In-Reply-To: <20131028135043.GP19466@laptop.lan> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13102903-1618-0000-0000-000004E13A9B Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Peter, On 10/28/2013 07:20 PM, Peter Zijlstra wrote: > On Thu, Oct 24, 2013 at 01:37:38PM +0530, Preeti U Murthy wrote: >> kernel/sched/core.c | 5 +++++ >> kernel/sched/fair.c | 38 ++++++++++++++++++++------------------ >> kernel/sched/sched.h | 1 + >> 3 files changed, 26 insertions(+), 18 deletions(-) >> >> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >> index c06b8d3..c540392 100644 >> --- a/kernel/sched/core.c >> +++ b/kernel/sched/core.c >> @@ -5271,6 +5271,7 @@ DEFINE_PER_CPU(struct sched_domain *, sd_llc); >> DEFINE_PER_CPU(int, sd_llc_size); >> DEFINE_PER_CPU(int, sd_llc_id); >> DEFINE_PER_CPU(struct sched_domain *, sd_numa); >> +DEFINE_PER_CPU(struct sched_domain *, sd_busy); >> >> static void update_top_cache_domain(int cpu) >> { >> @@ -5290,6 +5291,10 @@ static void update_top_cache_domain(int cpu) >> >> sd = lowest_flag_domain(cpu, SD_NUMA); >> rcu_assign_pointer(per_cpu(sd_numa, cpu), sd); >> + >> + sd = highest_flag_domain(cpu, SD_SHARE_PKG_RESOURCES); >> + if (sd) >> + rcu_assign_pointer(per_cpu(sd_busy, cpu), sd->parent); >> } >> >> /* >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index e9c9549..f66cfd9 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -6515,16 +6515,16 @@ static inline void nohz_balance_exit_idle(int cpu) >> static inline void set_cpu_sd_state_busy(void) >> { >> struct sched_domain *sd; >> + int cpu = smp_processor_id(); >> >> rcu_read_lock(); >> + sd = rcu_dereference(per_cpu(sd_busy, cpu)); >> >> if (!sd || !sd->nohz_idle) >> goto unlock; >> sd->nohz_idle = 0; >> >> + atomic_inc(&sd->groups->sgp->nr_busy_cpus); >> unlock: >> rcu_read_unlock(); >> } >> @@ -6532,16 +6532,16 @@ unlock: >> void set_cpu_sd_state_idle(void) >> { >> struct sched_domain *sd; >> + int cpu = smp_processor_id(); >> >> rcu_read_lock(); >> + sd = rcu_dereference(per_cpu(sd_busy, cpu)); >> >> if (!sd || sd->nohz_idle) >> goto unlock; >> sd->nohz_idle = 1; >> >> + atomic_dec(&sd->groups->sgp->nr_busy_cpus); >> unlock: >> rcu_read_unlock(); >> } > > Oh nice, that gets rid of the multiple atomics, and it nicely splits > this nohz logic into per topology groups -- now if only we could split > the rest too :-) I am sorry, I don't get you here. By the 'rest', do you refer to nohz_kick_needed() as below? Or am I missing something? > >> @@ -6748,6 +6748,8 @@ static inline int nohz_kick_needed(struct rq *rq, int cpu) >> { >> unsigned long now = jiffies; >> struct sched_domain *sd; >> + struct sched_group_power *sgp; >> + int nr_busy; >> >> if (unlikely(idle_cpu(cpu))) >> return 0; >> @@ -6773,22 +6775,22 @@ static inline int nohz_kick_needed(struct rq *rq, int cpu) >> goto need_kick; >> >> rcu_read_lock(); >> + sd = rcu_dereference(per_cpu(sd_busy, cpu)); >> >> + if (sd) { >> + sgp = sd->groups->sgp; >> + nr_busy = atomic_read(&sgp->nr_busy_cpus); >> >> + if (nr_busy > 1) >> goto need_kick_unlock; >> } > > OK, so far so good. > >> + >> + sd = highest_flag_domain(cpu, SD_ASYM_PACKING); >> + >> + if (sd && (cpumask_first_and(nohz.idle_cpus_mask, >> + sched_domain_span(sd)) < cpu)) >> + goto need_kick_unlock; >> + >> rcu_read_unlock(); >> return 0; > > This again is a bit sad; most archs will not have SD_ASYM_PACKING set at > all; this means that they all will do a complete (and pointless) sched > domain tree walk here. There will not be a 'complete' sched domain tree walk right? The iteration will break at the first level of the sched domain for those archs which do not have SD_ASYM_PACKING set at all. But it is true that doing a sched domain tree walk regularly is a bad idea, might as well update the domain with SD_ASYM_PACKING flag set once and query this domain when required. I will send out the patch with sd_asym domain introduced rather than the above. Thanks Regards Preeti U Murthy > > It would be much better to also introduce sd_asym and do the analogous > thing to the new sd_busy. >