From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Rusty Russell <rusty@rustcorp.com.au>,
"Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>,
Arjan van de Veen <arjan@infradead.org>,
Paul Turner <pjt@google.com>,
Richard Weinberger <rw@linutronix.de>,
Magnus Damm <magnus.damm@gmail.com>
Subject: Re: [patch 32/40] rcu: Convert rcutree to hotplug state machine
Date: Mon, 11 Feb 2013 16:01:01 -0800 [thread overview]
Message-ID: <20130212000100.GB2666@linux.vnet.ibm.com> (raw)
In-Reply-To: <20130131120743.656655375@linutronix.de>
On Thu, Jan 31, 2013 at 12:11:38PM -0000, Thomas Gleixner wrote:
> Do we really need so many states here ?
Well, all that RCU does for CPU_DYING is to do tracing, which could be
ditched. Required changes called out inline below.
All that the CPU_ONLINE and CPU_DOWN_PREPARE notifiers do is set
up affinity for the RCU-boost kthreads. These are unfortunately not
per-CPU kthreads, but perhaps something similar could be set up. This is
strictly a performance optimization, so the CPU_ONLINE notifier could
be replaced by having the kthread check which of its CPUs was online.
Unfortunately, the same is not true of CPU_DOWN_PREPARE because if the
kthread was too slow about it, the scheduler would get annoyed about a
kthread being runnable only on offlined CPUs.
It is not clear that this is worthwhile. Thoughts on other ways to
get this done?
Thanx, Paul
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
> include/linux/cpuhotplug.h | 18 ++++++++
> kernel/cpu.c | 12 +++++
> kernel/rcutree.c | 95 ++++++++++++++++++++-------------------------
> 3 files changed, 73 insertions(+), 52 deletions(-)
>
> Index: linux-2.6/include/linux/cpuhotplug.h
> ===================================================================
> --- linux-2.6.orig/include/linux/cpuhotplug.h
> +++ linux-2.6/include/linux/cpuhotplug.h
> @@ -12,6 +12,7 @@ enum cpuhp_states {
> CPUHP_PERF_PREPARE,
> CPUHP_SCHED_MIGRATE_PREP,
> CPUHP_WORKQUEUE_PREP,
> + CPUHP_RCUTREE_PREPARE,
> CPUHP_NOTIFY_PREPARE,
> CPUHP_NOTIFY_DEAD,
> CPUHP_CPUFREQ_DEAD,
> @@ -27,6 +28,7 @@ enum cpuhp_states {
> CPUHP_AP_ARM64_TIMER_STARTING,
> CPUHP_AP_KVM_STARTING,
> CPUHP_AP_NOTIFY_DYING,
> + CPUHP_AP_RCUTREE_DYING,
Drop this.
> CPUHP_AP_X86_TBOOT_DYING,
> CPUHP_AP_S390_VTIME_DYING,
> CPUHP_AP_SCHED_NOHZ_DYING,
> @@ -39,6 +41,7 @@ enum cpuhp_states {
> CPUHP_SCHED_MIGRATE_ONLINE,
> CPUHP_WORKQUEUE_ONLINE,
> CPUHP_CPUFREQ_ONLINE,
> + CPUHP_RCUTREE_ONLINE,
> CPUHP_NOTIFY_ONLINE,
> CPUHP_NOTIFY_DOWN_PREPARE,
> CPUHP_PERF_X86_UNCORE_ONLINE,
> @@ -147,4 +150,19 @@ int workqueue_prepare_cpu(unsigned int c
> int workqueue_online_cpu(unsigned int cpu);
> int workqueue_offline_cpu(unsigned int cpu);
>
> +/* RCUtree hotplug events */
> +#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
> +int rcutree_prepare_cpu(unsigned int cpu);
> +int rcutree_online_cpu(unsigned int cpu);
> +int rcutree_offline_cpu(unsigned int cpu);
> +int rcutree_dead_cpu(unsigned int cpu);
> +int rcutree_dying_cpu(unsigned int cpu);
And this...
> +#else
> +#define rcutree_prepare_cpu NULL
> +#define rcutree_online_cpu NULL
> +#define rcutree_offline_cpu NULL
> +#define rcutree_dead_cpu NULL
> +#define rcutree_dying_cpu NULL
And of course this.
> +#endif
> +
> #endif
> Index: linux-2.6/kernel/cpu.c
> ===================================================================
> --- linux-2.6.orig/kernel/cpu.c
> +++ linux-2.6/kernel/cpu.c
> @@ -755,6 +755,10 @@ static struct cpuhp_step cpuhp_bp_states
> .startup = workqueue_prepare_cpu,
> .teardown = NULL,
> },
> + [CPUHP_RCUTREE_PREPARE] = {
> + .startup = rcutree_prepare_cpu,
> + .teardown = rcutree_dead_cpu,
> + },
> [CPUHP_NOTIFY_PREPARE] = {
> .startup = notify_prepare,
> .teardown = NULL,
> @@ -787,6 +791,10 @@ static struct cpuhp_step cpuhp_bp_states
> .startup = workqueue_online_cpu,
> .teardown = workqueue_offline_cpu,
> },
> + [CPUHP_RCUTREE_ONLINE] = {
> + .startup = rcutree_online_cpu,
> + .teardown = rcutree_offline_cpu,
> + },
> [CPUHP_NOTIFY_ONLINE] = {
> .startup = notify_online,
> .teardown = NULL,
> @@ -813,6 +821,10 @@ static struct cpuhp_step cpuhp_ap_states
> .startup = NULL,
> .teardown = notify_dying,
> },
> + [CPUHP_AP_RCUTREE_DYING] = {
> + .startup = NULL,
> + .teardown = rcutree_dying_cpu,
> + },
> [CPUHP_AP_SCHED_NOHZ_DYING] = {
> .startup = NULL,
> .teardown = nohz_balance_exit_idle,
> Index: linux-2.6/kernel/rcutree.c
> ===================================================================
> --- linux-2.6.orig/kernel/rcutree.c
> +++ linux-2.6/kernel/rcutree.c
> @@ -2787,67 +2787,59 @@ rcu_init_percpu_data(int cpu, struct rcu
> mutex_unlock(&rsp->onoff_mutex);
> }
>
> -static void __cpuinit rcu_prepare_cpu(int cpu)
> +int __cpuinit rcutree_prepare_cpu(unsigned int cpu)
> {
> struct rcu_state *rsp;
>
> for_each_rcu_flavor(rsp)
> rcu_init_percpu_data(cpu, rsp,
> strcmp(rsp->name, "rcu_preempt") == 0);
> + rcu_prepare_kthreads(cpu);
> + return 0;
> }
>
> -/*
> - * Handle CPU online/offline notification events.
> - */
> -static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
> - unsigned long action, void *hcpu)
> +int __cpuinit rcutree_dead_cpu(unsigned int cpu)
> {
> - long cpu = (long)hcpu;
> - struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
> - struct rcu_node *rnp = rdp->mynode;
> struct rcu_state *rsp;
> - int ret = NOTIFY_OK;
>
> - trace_rcu_utilization("Start CPU hotplug");
> - switch (action) {
> - case CPU_UP_PREPARE:
> - case CPU_UP_PREPARE_FROZEN:
> - rcu_prepare_cpu(cpu);
> - rcu_prepare_kthreads(cpu);
> - break;
> - case CPU_ONLINE:
> - case CPU_DOWN_FAILED:
> - rcu_boost_kthread_setaffinity(rnp, -1);
> - break;
> - case CPU_DOWN_PREPARE:
> - if (nocb_cpu_expendable(cpu))
> - rcu_boost_kthread_setaffinity(rnp, cpu);
> - else
> - ret = NOTIFY_BAD;
> - break;
> - case CPU_DYING:
> - case CPU_DYING_FROZEN:
> - /*
> - * The whole machine is "stopped" except this CPU, so we can
> - * touch any data without introducing corruption. We send the
> - * dying CPU's callbacks to an arbitrarily chosen online CPU.
> - */
> - for_each_rcu_flavor(rsp)
> - rcu_cleanup_dying_cpu(rsp);
> - rcu_cleanup_after_idle(cpu);
> - break;
> - case CPU_DEAD:
> - case CPU_DEAD_FROZEN:
> - case CPU_UP_CANCELED:
> - case CPU_UP_CANCELED_FROZEN:
> - for_each_rcu_flavor(rsp)
> - rcu_cleanup_dead_cpu(cpu, rsp);
> - break;
> - default:
> - break;
> - }
> - trace_rcu_utilization("End CPU hotplug");
> - return ret;
> + for_each_rcu_flavor(rsp)
> + rcu_cleanup_dead_cpu(cpu, rsp);
> + return 0;
> +}
> +
> +static void __cpuinit rcutree_affinity_setting(unsigned int cpu, int outgoing)
> +{
> + struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
> +
> + rcu_boost_kthread_setaffinity(rdp->mynode, outgoing);
> +}
> +
> +int __cpuinit rcutree_online_cpu(unsigned int cpu)
> +{
> + rcutree_affinity_setting(cpu, -1);
> + return 0;
> +}
> +
> +int __cpuinit rcutree_offline_cpu(unsigned int cpu)
> +{
> + if (!nocb_cpu_expendable(cpu))
> + return -EINVAL;
> + rcutree_affinity_setting(cpu, cpu);
> + return 0;
> +}
> +
> +int __cpuinit rcutree_dying_cpu(unsigned int cpu)
> +{
> + struct rcu_state *rsp;
> + /*
> + * The whole machine is "stopped" except this CPU, so we can
> + * touch any data without introducing corruption. We send the
> + * dying CPU's callbacks to an arbitrarily chosen online CPU.
> + */
> + for_each_rcu_flavor(rsp)
> + rcu_cleanup_dying_cpu(rsp);
> + rcu_cleanup_after_idle(cpu);
> + return 0;
> }
And rcu_dying_cpu() above, along with both definitions of
rcu_cleanup_dying_cpu().
> /*
> @@ -3071,9 +3063,8 @@ void __init rcu_init(void)
> * this is called early in boot, before either interrupts
> * or the scheduler are operational.
> */
> - cpu_notifier(rcu_cpu_notify, 0);
> for_each_online_cpu(cpu)
> - rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
> + rcutree_prepare_cpu(cpu);
> check_cpu_stall_init();
> }
>
>
>
next prev parent reply other threads:[~2013-02-12 0:01 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-31 15:44 [patch 00/40] CPU hotplug rework - episode I Thomas Gleixner
2013-01-31 12:11 ` [patch 01/40] smpboot: Allow selfparking per cpu threads Thomas Gleixner
2013-02-09 0:29 ` Paul E. McKenney
2013-02-14 17:46 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2013-01-31 12:11 ` [patch 02/40] stop_machine: Store task reference in a separate per cpu variable Thomas Gleixner
2013-02-09 0:33 ` Paul E. McKenney
2013-02-14 17:47 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2013-01-31 12:11 ` [patch 03/40] stop_machine: Use smpboot threads Thomas Gleixner
2013-02-09 0:39 ` Paul E. McKenney
2013-02-14 17:49 ` [tip:smp/hotplug] " tip-bot for Thomas Gleixner
2013-01-31 12:11 ` [patch 04/40] cpu: Restructure FROZEN state handling Thomas Gleixner
2013-02-09 0:52 ` Paul E. McKenney
2014-10-09 16:53 ` Borislav Petkov
2013-01-31 12:11 ` [patch 05/40] cpu: Restructure cpu_down code Thomas Gleixner
2013-02-09 0:49 ` Paul E. McKenney
2014-10-09 17:05 ` Borislav Petkov
2013-01-31 12:11 ` [patch 06/40] cpu: hotplug: Split out cpu down functions Thomas Gleixner
2013-02-09 0:54 ` Paul E. McKenney
2013-01-31 12:11 ` [patch 07/40] cpu: hotplug: Convert to a state machine for the control processor Thomas Gleixner
2013-02-11 20:09 ` Paul E. McKenney
2013-01-31 12:11 ` [patch 08/40] cpu: hotplug: Convert the hotplugged processor work to a state machine Thomas Gleixner
2013-02-11 20:17 ` Paul E. McKenney
2013-01-31 12:11 ` [patch 10/40] sched: Convert to state machine callbacks Thomas Gleixner
2013-02-11 23:46 ` Paul E. McKenney
2013-01-31 12:11 ` [patch 09/40] cpu: hotplug: Implement setup/removal interface Thomas Gleixner
2013-02-01 13:44 ` Hillf Danton
2013-02-01 13:52 ` Thomas Gleixner
2013-01-31 12:11 ` [patch 11/40] x86: uncore: Move teardown callback to CPU_DEAD Thomas Gleixner
2013-01-31 12:11 ` [patch 12/40] x86: uncore: Convert to hotplug state machine Thomas Gleixner
2013-01-31 12:11 ` [patch 13/40] perf: " Thomas Gleixner
2013-01-31 12:11 ` [patch 14/40] x86: perf: Convert the core to the " Thomas Gleixner
2013-01-31 12:11 ` [patch 16/40] blackfin: perf: Convert hotplug notifier to " Thomas Gleixner
2013-01-31 12:11 ` [patch 15/40] x86: perf: Convert AMD IBS to hotplug " Thomas Gleixner
2013-01-31 12:11 ` [patch 17/40] powerpc: perf: Convert book3s notifier to state machine callbacks Thomas Gleixner
2013-01-31 12:11 ` [patch 18/40] s390: perf: Convert the hotplug " Thomas Gleixner
2013-01-31 12:11 ` [patch 19/40] sh: perf: Convert the hotplug notifiers " Thomas Gleixner
2013-01-31 12:11 ` [patch 21/40] sched: Convert the migration callback to hotplug states Thomas Gleixner
2013-01-31 12:11 ` [patch 20/40] perf: Remove perf cpu notifier code Thomas Gleixner
2013-01-31 12:11 ` [patch 22/40] workqueue: Convert to state machine callbacks Thomas Gleixner
2013-01-31 12:11 ` [patch 23/40] cpufreq: Convert to hotplug state machine Thomas Gleixner
2013-01-31 12:11 ` [patch 24/40] arm64: Convert generic timers " Thomas Gleixner
2013-01-31 12:11 ` [patch 25/40] arm: Convert VFP hotplug notifiers to " Thomas Gleixner
2013-01-31 12:11 ` [patch 26/40] arm: perf: Convert to hotplug " Thomas Gleixner
2013-01-31 12:11 ` [patch 27/40] virt: Convert kvm hotplug to " Thomas Gleixner
2013-01-31 12:11 ` [patch 28/40] cpuhotplug: Remove CPU_STARTING notifier Thomas Gleixner
2013-01-31 12:11 ` [patch 29/40] s390: Convert vtime to hotplug state machine Thomas Gleixner
2013-01-31 12:11 ` [patch 30/40] x86: tboot: Convert " Thomas Gleixner
2013-01-31 12:11 ` [patch 31/40] sched: Convert fair nohz balancer " Thomas Gleixner
2013-01-31 12:11 ` [patch 33/40] hrtimer: Convert " Thomas Gleixner
2013-01-31 12:11 ` [patch 32/40] rcu: Convert rcutree " Thomas Gleixner
2013-02-12 0:01 ` Paul E. McKenney [this message]
2013-02-12 15:50 ` Paul E. McKenney
2013-01-31 12:11 ` [patch 34/40] cpuhotplug: Remove CPU_DYING notifier Thomas Gleixner
2013-01-31 12:11 ` [patch 35/40] timers: Convert to hotplug state machine Thomas Gleixner
2013-01-31 12:11 ` [patch 36/40] profile: Convert ot " Thomas Gleixner
2013-01-31 12:11 ` [patch 37/40] x86: x2apic: Convert to cpu " Thomas Gleixner
2013-01-31 12:11 ` [patch 38/40] smp: Convert core to " Thomas Gleixner
2013-01-31 12:11 ` [patch 39/40] relayfs: Convert " Thomas Gleixner
2013-01-31 12:11 ` [patch 40/40] slab: " Thomas Gleixner
2013-01-31 20:23 ` [patch 00/40] CPU hotplug rework - episode I Andrew Morton
2013-01-31 21:48 ` Thomas Gleixner
2013-01-31 21:59 ` Linus Torvalds
2013-01-31 22:44 ` Thomas Gleixner
2013-01-31 22:55 ` Linus Torvalds
2013-02-01 10:51 ` Thomas Gleixner
2013-02-07 4:01 ` Rusty Russell
2013-02-09 0:28 ` Paul E. McKenney
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