LKML Archive on
 help / color / Atom feed
From: Konstantin Khlebnikov <>
To: Peter Zijlstra <>
Cc: Ingo Molnar <>,,
Subject: Re: [PATCH] sched/fair: initialize throttle_count for new task-groups lazily
Date: Wed, 22 Jun 2016 11:10:46 +0300
Message-ID: <> (raw)
In-Reply-To: <>

On 22.06.2016 00:10, Peter Zijlstra wrote:
> On Thu, Jun 16, 2016 at 03:57:01PM +0300, Konstantin Khlebnikov wrote:
>> Cgroup created inside throttled group must inherit current throttle_count.
>> Broken throttle_count allows to nominate throttled entries as a next buddy,
>> later this leads to null pointer dereference in pick_next_task_fair().
>> This patch initialize cfs_rq->throttle_count at first enqueue: laziness
>> allows to skip locking all rq at group creation. Lazy approach also allows
>> to skip full sub-tree scan at throttling hierarchy (not in this patch).
> You're talking about taking rq->lock in alloc_fair_sched_group(), right?
> We're about to go do that anyway... But I suppose for backports this
> makes sense. Doing it at creation time also avoids the issues Ben
> raised, right?

Yes, all will be fine. But for 8192-cores this will be disaster =)
throttle_count must be initialized after linking tg into lists. obviously.


  reply index

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-16 12:57 Konstantin Khlebnikov
2016-06-16 17:03 ` bsegall
2016-06-16 17:23   ` Konstantin Khlebnikov
2016-06-16 17:33     ` bsegall
2016-06-21 13:41 ` Konstantin Khlebnikov
2016-06-21 21:10 ` Peter Zijlstra
2016-06-22  8:10   ` Konstantin Khlebnikov [this message]
2016-06-22  8:23     ` Peter Zijlstra
2016-06-24  8:59 ` [tip:sched/urgent] sched/fair: Initialize " tip-bot for Konstantin Khlebnikov

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

LKML Archive on

Archives are clonable:
	git clone --mirror lkml/git/0.git
	git clone --mirror lkml/git/1.git
	git clone --mirror lkml/git/2.git
	git clone --mirror lkml/git/3.git
	git clone --mirror lkml/git/4.git
	git clone --mirror lkml/git/5.git
	git clone --mirror lkml/git/6.git
	git clone --mirror lkml/git/7.git
	git clone --mirror lkml/git/8.git
	git clone --mirror lkml/git/9.git
	git clone --mirror lkml/git/10.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 lkml lkml/ \
	public-inbox-index lkml

Example config snippet for mirrors

Newsgroup available over NNTP:

AGPL code for this site: git clone