[Devel] Re: [PATCH, v3 2/2] cgroups: introduce timer slack subsystem
Matt Helsley
matthltc at us.ibm.com
Wed Feb 2 21:46:16 PST 2011
On Wed, Feb 02, 2011 at 10:47:36PM +0200, Kirill A. Shutsemov wrote:
> From: Kirill A. Shutemov <kirill at shutemov.name>
>
> Provides a way of tasks grouping by timer slack value. Introduces per
> cgroup max and min timer slack value. When a task attaches to a cgroup,
> its timer slack value adjusts (if needed) to fit min-max range.
>
> It also provides a way to set timer slack value for all tasks in the
> cgroup at once.
>
> This functionality is useful in mobile devices where certain background
> apps are attached to a cgroup and minimum wakeups are desired.
>
> Signed-off-by: Kirill A. Shutemov <kirill at shutemov.name>
> Idea-by: Jacob Pan <jacob.jun.pan at linux.intel.com>
> ---
> include/linux/cgroup_subsys.h | 6 +
> include/linux/init_task.h | 4 +-
> init/Kconfig | 10 ++
> kernel/Makefile | 1 +
> kernel/cgroup_timer_slack.c | 242 +++++++++++++++++++++++++++++++++++++++++
> kernel/sys.c | 24 +++-
> 6 files changed, 280 insertions(+), 7 deletions(-)
> create mode 100644 kernel/cgroup_timer_slack.c
>
> 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/include/linux/init_task.h b/include/linux/init_task.h
> index caa151f..48eca8f 100644
> --- a/include/linux/init_task.h
> +++ b/include/linux/init_task.h
> @@ -124,6 +124,8 @@ extern struct cred init_cred;
> # define INIT_PERF_EVENTS(tsk)
> #endif
>
> +#define TIMER_SLACK_NS_DEFAULT 50000
> +
> /*
> * INIT_TASK is used to set up the first task table, touch at
> * your own risk!. Base=0, limit=0x1fffff (=2MB)
> @@ -177,7 +179,7 @@ extern struct cred init_cred;
> .cpu_timers = INIT_CPU_TIMERS(tsk.cpu_timers), \
> .fs_excl = ATOMIC_INIT(0), \
> .pi_lock = __RAW_SPIN_LOCK_UNLOCKED(tsk.pi_lock), \
> - .timer_slack_ns = 50000, /* 50 usec default slack */ \
> + .timer_slack_ns = TIMER_SLACK_NS_DEFAULT, \
> .pids = { \
> [PIDTYPE_PID] = INIT_PID_LINK(PIDTYPE_PID), \
> [PIDTYPE_PGID] = INIT_PID_LINK(PIDTYPE_PGID), \
> diff --git a/init/Kconfig b/init/Kconfig
> index be788c0..f21b4ce 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 subsystem"
> + help
> + Provides a way of tasks grouping by timer slack value.
> + Introduces per cgroup timer slack value which will override
> + the default timer slack value once a task is attached to a
> + cgroup.
> + It's useful in mobile devices where certain background apps
> + are attached to a cgroup and minimum wakeups are desired.
Again -- I don't think "minimum" is the right choice of words here.
> +
> config CGROUP_DEVICE
> bool "Device controller for cgroups"
> help
> diff --git a/kernel/Makefile b/kernel/Makefile
> index 353d3fe..0b60239 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..a343a50
> --- /dev/null
> +++ b/kernel/cgroup_timer_slack.c
> @@ -0,0 +1,242 @@
> +/*
> + * 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>
> +
> +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,
> +};
> +
> +int dummy_timer_slack_check(struct task_struct *task, unsigned long slack_ns);
The above should be "extern" shouldn't it? Also, I think there's a way
to eliminate it (more below).
> +extern int (*timer_slack_check)(struct task_struct *task,
> + unsigned long slack_ns);
> +
> +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 cgroup_timer_slack_check(struct task_struct *task,
> + unsigned long slack_ns)
nit: rename to cgroup_timer_slack_allowed() ?
> +{
> + struct cgroup_subsys_state *css;
> + struct timer_slack_cgroup *tslack_cgroup;
> +
> + css = task_subsys_state(task, timer_slack_subsys.subsys_id);
> + tslack_cgroup = container_of(css, struct timer_slack_cgroup, css);
> +
> + if (slack_ns < tslack_cgroup->min_slack_ns)
> + return -EPERM;
> + if (slack_ns > tslack_cgroup->max_slack_ns)
> + return -EPERM;
> + return 0;
> +}
> +
> +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_cgroup->max_slack_ns = parent->max_slack_ns;
> + } else {
> + tslack_cgroup->min_slack_ns = 0UL;
> + tslack_cgroup->max_slack_ns = ULONG_MAX;
> + }
> +
> + return &tslack_cgroup->css;
> +}
> +
> +static void tslack_cgroup_destroy(struct cgroup_subsys *subsys,
> + struct cgroup *cgroup)
> +{
> + kfree(cgroup_to_tslack_cgroup(cgroup));
> +}
> +
> +/*
> + * Adjust ->timer_slack_ns and ->default_max_slack_ns of the task to fit
> + * limits of the cgroup.
> + */
> +static void tslack_adjust_task(struct timer_slack_cgroup *tslack_cgroup,
> + struct task_struct *tsk)
> +{
> + if (tslack_cgroup->min_slack_ns > tsk->timer_slack_ns)
> + tsk->timer_slack_ns = tslack_cgroup->min_slack_ns;
> + else if (tslack_cgroup->max_slack_ns < tsk->timer_slack_ns)
> + tsk->timer_slack_ns = tslack_cgroup->max_slack_ns;
> +
> + if (tslack_cgroup->min_slack_ns > tsk->default_timer_slack_ns)
> + tsk->default_timer_slack_ns = tslack_cgroup->min_slack_ns;
> + else if (tslack_cgroup->max_slack_ns < tsk->default_timer_slack_ns)
> + tsk->default_timer_slack_ns = tslack_cgroup->max_slack_ns;
> +}
> +
> +static void tslack_cgroup_attach(struct cgroup_subsys *subsys,
> + struct cgroup *cgroup, struct cgroup *prev,
> + struct task_struct *tsk, bool threadgroup)
> +{
> + tslack_adjust_task(cgroup_to_tslack_cgroup(cgroup), tsk);
> +}
> +
> +static int tslack_write_set_slack_ns(struct cgroup *cgroup, struct cftype *cft,
> + u64 val)
> +{
> + struct timer_slack_cgroup *tslack_cgroup;
> + struct cgroup_iter it;
> + struct task_struct *task;
> +
> + tslack_cgroup = cgroup_to_tslack_cgroup(cgroup);
> + if (!val || val < tslack_cgroup->min_slack_ns ||
Why is a val of 0 disallowed? I know having slack is good, but for
an administrator or tool that doesn't care about number of wakeups
and cares more about wringing out performance a slack of
0 seems acceptable. Is this just here to be consistent with the
values passed in via prctl?
> + val > tslack_cgroup->max_slack_ns )
> + return -EINVAL;
Shouldn't it be EPERM and not EINVAL?
The write(2) man page says: "Other errors may occur, depending on the
object connected to fd." So I think EPERM is fine and more descriptive.
> +
> + /* Change timer slack value for all tasks in the cgroup */
> + cgroup_iter_start(cgroup, &it);
> + while ((task = cgroup_iter_next(cgroup, &it)))
> + task->timer_slack_ns = val;
> + cgroup_iter_end(cgroup, &it);
> +
> + return 0;
> +}
> +
> +static u64 tslack_read_range(struct cgroup *cgroup, struct cftype *cft)
> +{
> + struct timer_slack_cgroup *tslack_cgroup;
> +
> + tslack_cgroup = cgroup_to_tslack_cgroup(cgroup);
> + switch (cft->private) {
> + case TIMER_SLACK_MIN:
> + return tslack_cgroup->min_slack_ns;
> + case TIMER_SLACK_MAX:
> + return tslack_cgroup->max_slack_ns;
> + default:
> + BUG();
> + };
> +}
> +
> +static int tslack_write_range(struct cgroup *cgroup, struct cftype *cft,
> + u64 val)
> +{
> + struct timer_slack_cgroup *tslack_cgroup;
> + struct cgroup_iter it;
> + struct task_struct *task;
> +
> + if (!val)
> + return -EINVAL;
Same question re: 0 slack...
> +
> + tslack_cgroup = cgroup_to_tslack_cgroup(cgroup);
> + switch (cft->private) {
> + case TIMER_SLACK_MIN:
> + if (val > tslack_cgroup->max_slack_ns)
> + return -EINVAL;
> + tslack_cgroup->min_slack_ns = val;
> + break;
> + case TIMER_SLACK_MAX:
> + if (val < tslack_cgroup->min_slack_ns)
> + return -EINVAL;
> + tslack_cgroup->max_slack_ns = val;
> + break;
> + default:
> + BUG();
> + }
> +
> + /*
> + * Adjust timer slack value for all tasks in the cgroup to fit
> + * min-max range.
> + */
> + cgroup_iter_start(cgroup, &it);
> + while ((task = cgroup_iter_next(cgroup, &it)))
> + tslack_adjust_task(tslack_cgroup, task);
> + cgroup_iter_end(cgroup, &it);
> +
> + return 0;
> +}
> +
> +static struct cftype files[] = {
> + {
> + .name = "set_slack_ns",
> + .write_u64 = tslack_write_set_slack_ns,
> + },
> + {
> + .name = "min_slack_ns",
> + .private = TIMER_SLACK_MIN,
> + .read_u64 = tslack_read_range,
> + .write_u64 = tslack_write_range,
> + },
> + {
> + .name = "max_slack_ns",
> + .private = TIMER_SLACK_MAX,
> + .read_u64 = tslack_read_range,
> + .write_u64 = tslack_write_range,
> + },
> +};
Looks good, thanks!
> +
> +static int tslack_cgroup_populate(struct cgroup_subsys *subsys,
> + struct cgroup *cgroup)
> +{
> + return cgroup_add_files(cgroup, subsys, files, ARRAY_SIZE(files));
> +}
> +
> +struct cgroup_subsys timer_slack_subsys = {
> + .name = "timer_slack",
> + .module = THIS_MODULE,
> +#ifdef CONFIG_CGROUP_TIMER_SLACK
> + .subsys_id = timer_slack_subsys_id,
> +#endif
Uhh... why is the #ifdef necessary? Won't it always be true if we're
compiling this file?
> + .create = tslack_cgroup_create,
> + .destroy = tslack_cgroup_destroy,
> + .attach = tslack_cgroup_attach,
> + .populate = tslack_cgroup_populate,
> +};
> +
> +static int __init init_cgroup_timer_slack(void)
> +{
> + BUG_ON(timer_slack_check != dummy_timer_slack_check);
You could just save the old timer_slack_check value into a static pointer
and then restore it in exit_cgroup_timer_slack. That would eliminate the
need for one of the two EXPORTs below but you wouldn't be able to do this
BUG_ON check. I think that'd be a slight improvement.
> + timer_slack_check = cgroup_timer_slack_check;
> + return cgroup_load_subsys(&timer_slack_subsys);
Shouldn't you load the subsystem first then set the timer_slack_check
function pointer once you know that the load has succeeded?
> +}
> +
> +static void __exit exit_cgroup_timer_slack(void)
> +{
> + BUG_ON(timer_slack_check != cgroup_timer_slack_check);
> + timer_slack_check = dummy_timer_slack_check;
> + cgroup_unload_subsys(&timer_slack_subsys);
> +}
> +
> +module_init(init_cgroup_timer_slack);
> +module_exit(exit_cgroup_timer_slack);
> +MODULE_LICENSE("GPL");
> diff --git a/kernel/sys.c b/kernel/sys.c
> index 18da702..57322a7 100644
> --- a/kernel/sys.c
> +++ b/kernel/sys.c
> @@ -118,6 +118,16 @@ EXPORT_SYMBOL(cad_pid);
>
> void (*pm_power_off_prepare)(void);
>
> +int dummy_timer_slack_check(struct task_struct *task, unsigned long slack_ns)
> +{
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(dummy_timer_slack_check);
As described previously, I don't think EXPORT of dummy_timer_slack_check is
necessary.
> +
> +int (*timer_slack_check)(struct task_struct *task, unsigned long slack_ns) =
> + dummy_timer_slack_check;
> +EXPORT_SYMBOL_GPL(timer_slack_check);
> +
> /*
> * set the priority of a task
> * - the caller must hold the RCU read lock
> @@ -1694,12 +1704,14 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
> error = current->timer_slack_ns;
> break;
> case PR_SET_TIMERSLACK:
> - if (arg2 <= 0)
> - current->timer_slack_ns =
> - current->default_timer_slack_ns;
> - else
> - current->timer_slack_ns = arg2;
> - error = 0;
> + if (arg2 <= 0) {
> + me->timer_slack_ns = me->default_timer_slack_ns;
> + break;
> + }
> +
> + error = timer_slack_check(me, arg2);
> + if (!error)
> + me->timer_slack_ns = arg2;
> break;
> case PR_MCE_KILL:
> if (arg4 | arg5)
> --
> 1.7.3.5
>
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