From: "Srivatsa S. Bhat" <srivatsa.bhat@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
Oleg Nesterov <oleg@redhat.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Mel Gorman <mgorman@suse.de>, Rik van Riel <riel@redhat.com>,
Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
Ingo Molnar <mingo@kernel.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Linux-MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Steven Rostedt <rostedt@goodmis.org>,
Viresh Kumar <viresh.kumar@linaro.org>
Subject: Re: [PATCH] hotplug: Optimize {get,put}_online_cpus()
Date: Tue, 01 Oct 2013 23:44:55 +0530 [thread overview]
Message-ID: <524B111F.9060003@linux.vnet.ibm.com> (raw)
In-Reply-To: <20131001173615.GW3657@laptop.programming.kicks-ass.net>
On 10/01/2013 11:06 PM, Peter Zijlstra wrote:
> On Tue, Oct 01, 2013 at 10:41:15PM +0530, Srivatsa S. Bhat wrote:
>> However, as Oleg said, its definitely worth considering whether this proposed
>> change in semantics is going to hurt us in the future. CPU_POST_DEAD has certainly
>> proved to be very useful in certain challenging situations (commit 1aee40ac9c
>> explains one such example), so IMHO we should be very careful not to undermine
>> its utility.
>
> Urgh.. crazy things. I've always understood POST_DEAD to mean 'will be
> called at some time after the unplug' with no further guarantees. And my
> patch preserves that.
>
> Its not at all clear to me why cpufreq needs more; 1aee40ac9c certainly
> doesn't explain it.
>
Sorry if I was unclear - I didn't mean to say that cpufreq needs more guarantees
than that. I was just saying that the cpufreq code would need certain additional
changes/restructuring to accommodate the change in the semantics brought about
by this patch. IOW, it won't work as it is, but it can certainly be fixed.
My other point (unrelated to cpufreq) was this: POST_DEAD of course means
that it will be called after unplug, with hotplug lock dropped. But it also
provides the guarantee (in the existing code), that a *new* hotplug operation
won't start until the POST_DEAD stage is also completed. This patch doesn't seem
to honor that part. The concern I have is in cases like those mentioned by
Oleg - say you take a lock at DOWN_PREPARE and want to drop it at POST_DEAD;
or some other requirement that makes it important to finish a full hotplug cycle
before moving on to the next one. I don't really have such a requirement in mind
at present, but I was just trying to think what we would be losing with this
change...
But to reiterate, I believe cpufreq can be reworked so that it doesn't depend
on things such as the above. But I wonder if dropping that latter guarantee
is going to be OK, going forward.
Regards,
Srivatsa S. Bhat
> What's wrong with leaving a cleanup handle in percpu storage and
> effectively doing:
>
> struct cpu_destroy {
> void (*destroy)(void *);
> void *args;
> };
>
> DEFINE_PER_CPU(struct cpu_destroy, cpu_destroy);
>
> POST_DEAD:
> {
> struct cpu_destroy x = per_cpu(cpu_destroy, cpu);
> if (x.destroy)
> x.destroy(x.arg);
> }
>
> POST_DEAD cannot fail; so CPU_DEAD/CPU_DOWN_PREPARE can simply assume it
> will succeed; it has to.
>
> The cpufreq situation simply doesn't make any kind of sense to me.
>
>
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next prev parent reply other threads:[~2013-10-01 18:19 UTC|newest]
Thread overview: 182+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-10 9:31 [PATCH 0/50] Basic scheduler support for automatic NUMA balancing V7 Mel Gorman
2013-09-10 9:31 ` [PATCH 01/50] sched: monolithic code dump of what is being pushed upstream Mel Gorman
2013-09-11 0:58 ` Joonsoo Kim
2013-09-11 3:11 ` Hillf Danton
2013-09-13 8:11 ` Mel Gorman
2013-09-10 9:31 ` [PATCH 02/50] mm: numa: Document automatic NUMA balancing sysctls Mel Gorman
2013-09-10 9:31 ` [PATCH 03/50] sched, numa: Comment fixlets Mel Gorman
2013-09-10 9:31 ` [PATCH 04/50] mm: numa: Do not account for a hinting fault if we raced Mel Gorman
2013-09-10 9:31 ` [PATCH 05/50] mm: Wait for THP migrations to complete during NUMA hinting faults Mel Gorman
2013-09-10 9:31 ` [PATCH 06/50] mm: Prevent parallel splits during THP migration Mel Gorman
2013-09-10 9:31 ` [PATCH 07/50] mm: Account for a THP NUMA hinting update as one PTE update Mel Gorman
2013-09-16 12:36 ` Peter Zijlstra
2013-09-16 13:39 ` Rik van Riel
2013-09-16 14:54 ` Peter Zijlstra
2013-09-16 16:11 ` Mel Gorman
2013-09-16 16:37 ` Peter Zijlstra
2013-09-10 9:31 ` [PATCH 08/50] mm: numa: Sanitize task_numa_fault() callsites Mel Gorman
2013-09-10 9:31 ` [PATCH 09/50] mm: numa: Do not migrate or account for hinting faults on the zero page Mel Gorman
2013-09-10 9:31 ` [PATCH 10/50] sched: numa: Mitigate chance that same task always updates PTEs Mel Gorman
2013-09-10 9:31 ` [PATCH 11/50] sched: numa: Continue PTE scanning even if migrate rate limited Mel Gorman
2013-09-10 9:31 ` [PATCH 12/50] Revert "mm: sched: numa: Delay PTE scanning until a task is scheduled on a new node" Mel Gorman
2013-09-10 9:31 ` [PATCH 13/50] sched: numa: Initialise numa_next_scan properly Mel Gorman
2013-09-10 9:31 ` [PATCH 14/50] sched: Set the scan rate proportional to the memory usage of the task being scanned Mel Gorman
2013-09-16 15:18 ` Peter Zijlstra
2013-09-16 15:40 ` Mel Gorman
2013-09-10 9:31 ` [PATCH 15/50] sched: numa: Correct adjustment of numa_scan_period Mel Gorman
2013-09-10 9:31 ` [PATCH 16/50] mm: Only flush TLBs if a transhuge PMD is modified for NUMA pte scanning Mel Gorman
2013-09-10 9:31 ` [PATCH 17/50] mm: Do not flush TLB during protection change if !pte_present && !migration_entry Mel Gorman
2013-09-16 16:35 ` Peter Zijlstra
2013-09-17 17:00 ` Mel Gorman
2013-09-10 9:31 ` [PATCH 18/50] sched: numa: Slow scan rate if no NUMA hinting faults are being recorded Mel Gorman
2013-09-10 9:31 ` [PATCH 19/50] sched: Track NUMA hinting faults on per-node basis Mel Gorman
2013-09-10 9:32 ` [PATCH 20/50] sched: Select a preferred node with the most numa hinting faults Mel Gorman
2013-09-10 9:32 ` [PATCH 21/50] sched: Update NUMA hinting faults once per scan Mel Gorman
2013-09-10 9:32 ` [PATCH 22/50] sched: Favour moving tasks towards the preferred node Mel Gorman
2013-09-10 9:32 ` [PATCH 23/50] sched: Resist moving tasks towards nodes with fewer hinting faults Mel Gorman
2013-09-10 9:32 ` [PATCH 24/50] sched: Reschedule task on preferred NUMA node once selected Mel Gorman
2013-09-10 9:32 ` [PATCH 25/50] sched: Add infrastructure for split shared/private accounting of NUMA hinting faults Mel Gorman
2013-09-10 9:32 ` [PATCH 26/50] sched: Check current->mm before allocating NUMA faults Mel Gorman
2013-09-10 9:32 ` [PATCH 27/50] mm: numa: Scan pages with elevated page_mapcount Mel Gorman
2013-09-12 2:10 ` Hillf Danton
2013-09-13 8:11 ` Mel Gorman
2013-09-10 9:32 ` [PATCH 28/50] sched: Remove check that skips small VMAs Mel Gorman
2013-09-10 9:32 ` [PATCH 29/50] sched: Set preferred NUMA node based on number of private faults Mel Gorman
2013-09-10 9:32 ` [PATCH 30/50] sched: Do not migrate memory immediately after switching node Mel Gorman
2013-09-10 9:32 ` [PATCH 31/50] sched: Avoid overloading CPUs on a preferred NUMA node Mel Gorman
2013-09-10 9:32 ` [PATCH 32/50] sched: Retry migration of tasks to CPU on a preferred node Mel Gorman
2013-09-10 9:32 ` [PATCH 33/50] sched: numa: increment numa_migrate_seq when task runs in correct location Mel Gorman
2013-09-10 9:32 ` [PATCH 34/50] sched: numa: Do not trap hinting faults for shared libraries Mel Gorman
2013-09-17 2:02 ` 答复: " 张天飞
2013-09-17 8:05 ` ????: " Mel Gorman
2013-09-17 8:22 ` Figo.zhang
2013-09-10 9:32 ` [PATCH 35/50] mm: numa: Only trap pmd hinting faults if we would otherwise trap PTE faults Mel Gorman
2013-09-10 9:32 ` [PATCH 36/50] stop_machine: Introduce stop_two_cpus() Mel Gorman
2013-09-10 9:32 ` [PATCH 37/50] sched: Introduce migrate_swap() Mel Gorman
2013-09-17 14:30 ` [PATCH] hotplug: Optimize {get,put}_online_cpus() Peter Zijlstra
2013-09-17 16:20 ` Mel Gorman
2013-09-17 16:45 ` Peter Zijlstra
2013-09-18 15:49 ` Peter Zijlstra
2013-09-19 14:32 ` Peter Zijlstra
2013-09-21 16:34 ` Oleg Nesterov
2013-09-21 19:13 ` Oleg Nesterov
2013-09-23 9:29 ` Peter Zijlstra
2013-09-23 17:32 ` Oleg Nesterov
2013-09-24 20:24 ` Peter Zijlstra
2013-09-24 21:02 ` Peter Zijlstra
2013-09-25 15:55 ` Oleg Nesterov
2013-09-25 16:59 ` Paul E. McKenney
2013-09-25 17:43 ` Peter Zijlstra
2013-09-25 17:50 ` Oleg Nesterov
2013-09-25 18:40 ` Peter Zijlstra
2013-09-25 21:22 ` Paul E. McKenney
2013-09-26 11:10 ` Peter Zijlstra
[not found] ` <20130926155321.GA4342@redhat.com>
2013-09-26 16:13 ` Peter Zijlstra
2013-09-26 16:14 ` Oleg Nesterov
2013-09-26 16:40 ` Peter Zijlstra
2013-09-26 16:58 ` Oleg Nesterov
2013-09-26 17:50 ` Peter Zijlstra
2013-09-27 18:15 ` Oleg Nesterov
2013-09-27 20:41 ` Peter Zijlstra
2013-09-28 12:48 ` Oleg Nesterov
2013-09-28 14:47 ` Peter Zijlstra
2013-09-28 16:31 ` Oleg Nesterov
2013-09-30 20:11 ` Rafael J. Wysocki
2013-10-01 17:11 ` Srivatsa S. Bhat
2013-10-01 17:36 ` Peter Zijlstra
2013-10-01 17:45 ` Oleg Nesterov
2013-10-01 17:56 ` Peter Zijlstra
2013-10-01 18:07 ` Oleg Nesterov
2013-10-01 19:05 ` Paul E. McKenney
2013-10-02 12:16 ` Oleg Nesterov
2013-10-02 9:08 ` Peter Zijlstra
2013-10-02 12:13 ` Oleg Nesterov
2013-10-02 12:25 ` Peter Zijlstra
2013-10-02 13:31 ` Peter Zijlstra
2013-10-02 14:00 ` Oleg Nesterov
2013-10-02 15:17 ` Peter Zijlstra
2013-10-02 16:31 ` Oleg Nesterov
2013-10-02 17:52 ` Paul E. McKenney
2013-10-01 19:03 ` Srivatsa S. Bhat
2013-10-01 18:14 ` Srivatsa S. Bhat [this message]
2013-10-01 18:56 ` Srivatsa S. Bhat
2013-10-02 10:14 ` Srivatsa S. Bhat
2013-09-28 20:46 ` Paul E. McKenney
2013-10-01 3:56 ` Paul E. McKenney
2013-10-01 14:14 ` Oleg Nesterov
2013-10-01 14:45 ` Paul E. McKenney
2013-10-01 14:48 ` Peter Zijlstra
2013-10-01 15:24 ` Paul E. McKenney
2013-10-01 15:34 ` Oleg Nesterov
2013-10-01 15:00 ` Oleg Nesterov
2013-09-29 13:56 ` Oleg Nesterov
2013-10-01 15:38 ` Paul E. McKenney
2013-10-01 15:40 ` Oleg Nesterov
2013-10-01 20:40 ` Paul E. McKenney
2013-09-23 14:50 ` Steven Rostedt
2013-09-23 14:54 ` Peter Zijlstra
2013-09-23 15:13 ` Steven Rostedt
2013-09-23 15:22 ` Peter Zijlstra
2013-09-23 15:59 ` Steven Rostedt
2013-09-23 16:02 ` Peter Zijlstra
2013-09-23 15:50 ` Paul E. McKenney
2013-09-23 16:01 ` Peter Zijlstra
2013-09-23 17:04 ` Paul E. McKenney
2013-09-23 17:30 ` Peter Zijlstra
2013-09-23 17:50 ` Oleg Nesterov
2013-09-24 12:38 ` Peter Zijlstra
2013-09-24 14:42 ` Paul E. McKenney
2013-09-24 16:09 ` Peter Zijlstra
2013-09-24 16:31 ` Oleg Nesterov
2013-09-24 21:09 ` Paul E. McKenney
2013-09-24 16:03 ` Oleg Nesterov
2013-09-24 16:43 ` Steven Rostedt
2013-09-24 17:06 ` Oleg Nesterov
2013-09-24 17:47 ` Paul E. McKenney
2013-09-24 18:00 ` Oleg Nesterov
2013-09-24 20:35 ` Peter Zijlstra
2013-09-25 15:16 ` Oleg Nesterov
2013-09-25 15:35 ` Peter Zijlstra
2013-09-25 16:33 ` Oleg Nesterov
2013-09-24 16:49 ` Paul E. McKenney
2013-09-24 16:54 ` Peter Zijlstra
2013-09-24 17:02 ` Oleg Nesterov
2013-09-24 16:51 ` Peter Zijlstra
2013-09-24 16:39 ` Steven Rostedt
2013-09-29 18:36 ` [RFC] introduce synchronize_sched_{enter,exit}() Oleg Nesterov
2013-09-29 20:01 ` Paul E. McKenney
2013-09-30 12:42 ` Oleg Nesterov
2013-09-29 21:34 ` Steven Rostedt
2013-09-30 13:03 ` Oleg Nesterov
2013-09-30 12:59 ` Peter Zijlstra
2013-09-30 14:24 ` Peter Zijlstra
2013-09-30 15:06 ` Peter Zijlstra
2013-09-30 16:58 ` Oleg Nesterov
2013-09-30 16:38 ` Oleg Nesterov
2013-10-02 14:41 ` Peter Zijlstra
2013-10-03 7:04 ` Ingo Molnar
2013-10-03 7:43 ` Peter Zijlstra
2013-09-17 14:32 ` [PATCH 37/50] sched: Introduce migrate_swap() Peter Zijlstra
2013-09-10 9:32 ` [PATCH 38/50] sched: numa: Use a system-wide search to find swap/migration candidates Mel Gorman
2013-09-10 9:32 ` [PATCH 39/50] sched: numa: Favor placing a task on the preferred node Mel Gorman
2013-09-10 9:32 ` [PATCH 40/50] mm: numa: Change page last {nid,pid} into {cpu,pid} Mel Gorman
2013-09-10 9:32 ` [PATCH 41/50] sched: numa: Use {cpu, pid} to create task groups for shared faults Mel Gorman
2013-09-12 12:42 ` Hillf Danton
2013-09-12 14:40 ` Mel Gorman
2013-09-12 12:45 ` Hillf Danton
2013-09-10 9:32 ` [PATCH 42/50] sched: numa: Report a NUMA task group ID Mel Gorman
2013-09-10 9:32 ` [PATCH 43/50] mm: numa: Do not group on RO pages Mel Gorman
2013-09-10 9:32 ` [PATCH 44/50] sched: numa: stay on the same node if CLONE_VM Mel Gorman
2013-09-10 9:32 ` [PATCH 45/50] sched: numa: use group fault statistics in numa placement Mel Gorman
2013-09-10 9:32 ` [PATCH 46/50] sched: numa: Prevent parallel updates to group stats during placement Mel Gorman
2013-09-20 9:55 ` Peter Zijlstra
2013-09-20 12:31 ` Mel Gorman
2013-09-20 12:36 ` Peter Zijlstra
2013-09-20 13:31 ` Mel Gorman
2013-09-10 9:32 ` [PATCH 47/50] sched: numa: add debugging Mel Gorman
2013-09-10 9:32 ` [PATCH 48/50] sched: numa: Decide whether to favour task or group weights based on swap candidate relationships Mel Gorman
2013-09-10 9:32 ` [PATCH 49/50] sched: numa: fix task or group comparison Mel Gorman
2013-09-10 9:32 ` [PATCH 50/50] sched: numa: Avoid migrating tasks that are placed on their preferred node Mel Gorman
2013-09-11 2:03 ` [PATCH 0/50] Basic scheduler support for automatic NUMA balancing V7 Rik van Riel
2013-09-14 2:57 ` Bob Liu
2013-09-30 10:30 ` Mel Gorman
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