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Re: [PATCH, v6 3/3] cgroups: introduce timer slack controller [message #41682 is a reply to message #41678] Mon, 14 February 2011 13:59 Go to previous messageGo to previous message
Matt Helsley is currently offline  Matt Helsley
Messages: 86
Registered: August 2006
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On Mon, Feb 14, 2011 at 03:06:27PM +0200, Kirill A. Shutsemov wrote:
> From: Kirill A. Shutemov <kirill@shutemov.name>
>
> Every task_struct has timer_slack_ns value. This value uses to round up
> poll() and select() timeout values. This feature can be useful in
> mobile environment where combined wakeups are desired.
>
> cgroup subsys "timer_slack" implement timer slack controller. It
> provides a way to group tasks by timer slack value and manage the
> value of group's tasks.
>
> Idea-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
> ---
> Documentation/cgroups/timer_slack.txt | 93 +++++++++++
> include/linux/cgroup_subsys.h | 6 +
> init/Kconfig | 10 ++
> kernel/Makefile | 1 +
> kernel/cgroup_timer_slack.c | 285 +++++++++++++++++++++++++++++++++
> 5 files changed, 395 insertions(+), 0 deletions(-)
> create mode 100644 Documentation/cgroups/timer_slack.txt
> create mode 100644 kernel/cgroup_timer_slack.c
>
> diff --git a/Documentation/cgroups/timer_slack.txt b/Documentation/cgroups/timer_slack.txt
> new file mode 100644
> index 0000000..e7ec2f3
> --- /dev/null
> +++ b/Documentation/cgroups/timer_slack.txt
> @@ -0,0 +1,93 @@
> +Timer Slack Controller
> +=====================
> +
> +Overview
> +--------
> +
> +Every task_struct has timer_slack_ns value. This value uses to round up
> +poll() and select() timeout values. This feature can be useful in
> +mobile environment where combined wakeups are desired.
> +
> +cgroup subsys "timer_slack" implement timer slack controller. It
> +provides a way to group tasks by timer slack value and manage the
> +value of group's tasks.
> +
> +
> +User interface
> +--------------
> +
> +To get timer slack controller functionality you need to enable it in
> +kernel configuration:
> +
> +CONFIG_CGROUP_TIMER_SLACK=y
> +
> +or if you want to compile it as module:
> +
> +CONFIG_CGROUP_TIMER_SLACK=m
> +
> +The controller provides three files in cgroup directory:
> +
> +# mount -t cgroup -o timer_slack none /sys/fs/cgroup
> +# ls /sys/fs/cgroup/timer_slack.*
> +/sys/fs/cgroup/timer_slack.max_slack_ns
> +/sys/fs/cgroup/timer_slack.min_slack_ns
> +/sys/fs/cgroup/timer_slack.set_slack_ns
> +
> +timer_slack.min_slack_ns and timer_slack.set_slack_ns specify allowed
> +range of timer slack for tasks in cgroup. By default it unlimited:
> +
> +# cat /sys/fs/cgroup/timer_slack.min_slack_ns
> +0
> +# cat /sys/fs/cgroup/timer_slack.max_slack_ns
> +4294967295
> +
> +You can specify limits you want:
> +
> +# echo 50000 > /sys/fs/cgroup/timer_slack.min_slack_ns
> +# echo 1000000 > /sys/fs/cgroup/timer_slack.max_slack_ns
> +# cat /sys/fs/cgroup/timer_slack.{min,max}_slack_ns
> +50000
> +1000000
> +
> +Timer slack value of all tasks of the cgroup will be adjusted to fit
> +min-max range.
> +
> +If a task will try to call prctl() to change timer slack value out of
> +the range it get -EPERM.
> +
> +You can change timer slack value of all tasks of the cgroup at once:
> +
> +# echo 70000 > /sys/fs/cgroup/timer_slack.set_slack_ns
> +
> +Timer slack controller supports hierarchical groups. The only rule:
> +parent's limit range should be wider or equal to child's. Sibling
> +cgroups can have overlapping min-max range.
> +
> + (root: 50000 - 1000000)
> + / \
> + (a: 50000 - 50000) (b: 500000 - 1000000)
> + / \
> + (c: 500000 - 900000) (d: 700000 - 800000)
> +
> +# mkdir /sys/fs/cgroup/a
> +# echo 50000 > /sys/fs/cgroup/a/timer_slack.max_slack_ns
> +# cat /sys/fs/cgroup/a/timer_slack.{min,max}_slack_ns
> +50000
> +50000
> +# mkdir /sys/fs/cgroup/b
> +# echo 500000 > /sys/fs/cgroup/b/timer_slack.min_slack_ns
> +# cat /sys/fs/cgroup/b/timer_slack.{min,max}_slack_ns
> +500000
> +1000000
> +# mkdir /sys/fs/cgroup/b/c
> +# echo 900000 > /sys/fs/cgroup/b/c/timer_slack.max_slack_ns
> +# cat /sys/fs/cgroup/b/c/timer_slack.{min,max}_slack_ns
> +500000
> +900000
> +# mkdir /sys/fs/cgroup/b/d
> +# echo 700000 > /sys/fs/cgroup/b/d/timer_slack.min_slack_ns
> +# echo 800000 > /sys/fs/cgroup/b/d/timer_slack.max_slack_ns
> +# cat /sys/fs/cgroup/b/d/timer_slack.{min,max}_slack_ns
> +700000
> +800000
> +
> diff --git a/include/linux/cgroup_subsys.h b/include/linux/cgroup_subsys.h
> index ccefff0..e399228 100644
> --- a/include/linux/cgroup_subsys.h
> +++ b/include/linux/cgroup_subsys.h
> @@ -66,3 +66,9 @@ SUBSYS(blkio)
> #endif
>
> /* */
> +
> +#ifdef CONFIG_CGROUP_TIMER_SLACK
> +SUBSYS(timer_slack)
> +#endif
> +
> +/* */
> diff --git a/init/Kconfig b/init/Kconfig
> index be788c0..bb54ae9 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -596,6 +596,16 @@ config CGROUP_FREEZER
> Provides a way to freeze and unfreeze all tasks in a
> cgroup.
>
> +config CGROUP_TIMER_SLACK
> + tristate "Timer slack cgroup controller"
> + help
> + Provides a way of tasks grouping by timer slack value.
> + Every timer slack cgroup has min and max slack value. Task's
> + timer slack value will be adjusted to fit min-max range once
> + the task attached to the cgroup.
> + It's useful in mobile devices where certain background apps
> + are attached to a cgroup and combined wakeups are desired.
> +
> config CGROUP_DEVICE
> bool "Device controller for cgroups"
> help
> diff --git a/kernel/Makefile b/kernel/Makefile
> index aa43e63..0e660c5 100644
> --- a/kernel/Makefile
> +++ b/kernel/Makefile
> @@ -61,6 +61,7 @@ obj-$(CONFIG_BACKTRACE_SELF_TEST) += backtracetest.o
> obj-$(CONFIG_COMPAT) += compat.o
> obj-$(CONFIG_CGROUPS) += cgroup.o
> obj-$(CONFIG_CGROUP_FREEZER) += cgroup_freezer.o
> +obj-$(CONFIG_CGROUP_TIMER_SLACK) += cgroup_timer_slack.o
> obj-$(CONFIG_CPUSETS) += cpuset.o
> obj-$(CONFIG_CGROUP_NS) += ns_cgroup.o
> obj-$(CONFIG_UTS_NS) += utsname.o
> diff --git a/kernel/cgroup_timer_slack.c b/kernel/cgroup_timer_slack.c
> new file mode 100644
> index 0000000..ec63700
> --- /dev/null
> +++ b/kernel/cgroup_timer_slack.c
> @@ -0,0 +1,285 @@
> +/*
> + * cgroup_timer_slack.c - control group timer slack subsystem
> + *
> + * Copyright Nokia Corparation, 2011
> + * Author: Kirill A. Shutemov
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + */
> +#include <linux/cgroup.h>
> +#include <linux/init_task.h>
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +#include <linux/rcupdate.h>
> +
> +struct cgroup_subsys timer_slack_subsys;
> +struct timer_slack_cgroup {
> + struct cgroup_subsys_state css;
> + unsigned long min_slack_ns;
> + unsigned long max_slack_ns;
> +};
> +
> +enum {
> + TIMER_SLACK_MIN,
> + TIMER_SLACK_MAX,
> +};
> +
> +static struct timer_slack_cgroup *cgroup_to_tslack_cgroup(struct cgroup *cgroup)
> +{
> + struct cgroup_subsys_state *css;
> +
> + css = cgroup_subsys_state(cgroup, timer_slack_subsys.subsys_id);
> + return container_of(css, struct timer_slack_cgroup, css);
> +}
> +
> +static int is_timer_slack_allowed(struct timer_slack_cgroup *tslack_cgroup,
> + unsigned long slack_ns)
> +{
> + if (slack_ns < tslack_cgroup->min_slack_ns ||
> + slack_ns > tslack_cgroup->max_slack_ns)
> + return false;
> + return true;
> +}
> +
> +static int cgroup_timer_slack_check(struct notifier_block *nb,
> + unsigned long slack_ns, void *data)
> +{
> + struct cgroup_subsys_state *css;
> + struct timer_slack_cgroup *tslack_cgroup;
> +
> + /* XXX: lockdep false positive? */
> + rcu_read_lock();
> + css = task_subsys_state(current, timer_slack_subsys.subsys_id);
> + tslack_cgroup = container_of(css, struct timer_slack_cgroup, css);
> + rcu_read_unlock();
> +
> + if (!is_timer_slack_allowed(tslack_cgroup, slack_ns))

I think this test -- or at least accesses to the cgroup's min/max values
-- needs to be in the rcu_read_lock() else there is a race between the
notifier call from the context of the task calling prctl() and the context
of the task writing to the cgroup's (min|max)_slack_ns files.

> + return notifier_from_errno(-EPERM);
> + return NOTIFY_OK;
> +}
> +
> +static struct notifier_block cgroup_timer_slack_nb = {
> + .notifier_call = cgroup_timer_slack_check,
> +};
> +
> +static struct cgroup_subsys_state *
> +tslack_cgroup_create(struct cgroup_subsys *subsys, struct cgroup *cgroup)
> +{
> + struct timer_slack_cgroup *tslack_cgroup;
> +
> + tslack_cgroup = kmalloc(sizeof(*tslack_cgroup), GFP_KERNEL);
> + if (!tslack_cgroup)
> + return ERR_PTR(-ENOMEM);
> +
> + if (cgroup->parent) {
> + struct timer_slack_cgroup *parent;
> + parent = cgroup_to_tslack_cgroup(cgroup->parent);
> + tslack_cgroup->min_slack_ns = parent->min_slack_ns;
> + tslack_cgrou ...

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