Home » Mailing lists » Devel » Re: [PATCH 1/1, v7] cgroup/freezer: add per freezer duty ratio control
| Re: [PATCH 1/1, v7] cgroup/freezer: add per freezer duty ratio control [message #42075 is a reply to message #41645] |
Mon, 14 February 2011 19:41  |
jacob.jun.pan
Messages: 40
Registered: December 2010
|
Member |
|
|
On Sat, 12 Feb 2011 15:29:07 -0800
Matt Helsley <matthltc@us.ibm.com> wrote:
> On Fri, Feb 11, 2011 at 11:10:44AM -0800,
> jacob.jun.pan@linux.intel.com wrote:
> > From: Jacob Pan <jacob.jun.pan@linux.intel.com>
> >
> > Freezer subsystem is used to manage batch jobs which can start
> > stop at the same time. However, sometime it is desirable to let
> > the kernel manage the freezer state automatically with a given
> > duty ratio.
> > For example, if we want to reduce the time that backgroup apps
> > are allowed to run we can put them into a freezer subsystem and
> > set the kernel to turn them THAWED/FROZEN at given duty ratio.
> >
> > This patch introduces two file nodes under cgroup
> > freezer.duty_ratio_pct and freezer.period_sec
>
> Again: I don't think this is the right approach in the long term.
> It would be better not to add this interface and instead enable the
> cpu cgroup subsystem for non-rt tasks using a similar duty ratio
> concept..
>
> Nevertheless, I've added some feedback on the code for you here :).
>
Thanks for the thorough review, really appreciated.
> >
> > Usage example: set period to be 5 seconds and frozen duty ratio 90%
> > [root@localhost aoa]# echo 90 > freezer.duty_ratio_pct
> > [root@localhost aoa]# echo 5000 > freezer.period_ms
> >
> > Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> > ---
> > Documentation/cgroups/freezer-subsystem.txt | 23 ++++
> > kernel/cgroup_freezer.c | 153
> > ++++++++++++++++++++++++++- 2 files changed, 174 insertions(+), 2
> > deletions(-)
> >
> > diff --git a/Documentation/cgroups/freezer-subsystem.txt
> > b/Documentation/cgroups/freezer-subsystem.txt index
> > 41f37fe..2022b32 100644 ---
> > a/Documentation/cgroups/freezer-subsystem.txt +++
> > b/Documentation/cgroups/freezer-subsystem.txt @@ -100,3 +100,26 @@
> > things happens: and returns EINVAL)
> > 3) The tasks that blocked the cgroup from entering the
> > "FROZEN" state disappear from the cgroup's set of tasks.
> > +
> > +In embedded systems, it is desirable to manage group of
> > applications +for power saving. E.g. tasks that are not in the
> > foreground may be +frozen and unfrozen periodically to save power
> > without affecting user +experience. In this case, user/management
> > software can attach tasks +into freezer cgroup then specify duty
> > ratio and period that the +managed tasks are allowed to run.
> > +
> > +Usage example:
> > +Assuming freezer cgroup is already mounted, application being
> > managed +are included the "tasks" file node of the given freezer
> > cgroup. +To make the tasks frozen at 90% of the time every 5
> > seconds, do: +
> > +[root@localhost ]# echo 90 > freezer.duty_ratio_pct
> > +[root@localhost ]# echo 5000 > freezer.period_ms
> > +
> > +After that, the application in this freezer cgroup will only be
> > +allowed to run at the following pattern.
> > + __ __ __
> > + | |<-- 90% frozen -->| | | |
> > +____| |__________________| |__________________| |_____
> > +
> > + |<---- 5 seconds ---->|
>
> So most of the time I've been reviewing this I managed to invert it!
> I imagined "duty" meant the tasks were "on duty" ie runnable ie
> thawed. But according this this documentation it's the opposite...
>
My logic is that since this is a freezer, so positive logic should be
frozen instead of thaw.
> I've reviewed my review and now my comments are consistent with the
> above. :) However it makes me wonder if there are better names which
> would avoid this confusion.
>
How about frozen_time_pct?
> > diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
> > index e7bebb7..aaa91ca 100644
> > --- a/kernel/cgroup_freezer.c
> > +++ b/kernel/cgroup_freezer.c
> > @@ -21,6 +21,7 @@
> > #include <linux/uaccess.h>
> > #include <linux/freezer.h>
> > #include <linux/seq_file.h>
> > +#include <linux/kthread.h>
> >
> > enum freezer_state {
> > CGROUP_THAWED = 0,
> > @@ -28,12 +29,35 @@ enum freezer_state {
> > CGROUP_FROZEN,
> > };
> >
> > +enum duty_ratio_params {
> > + FREEZER_DUTY_RATIO = 0,
> > + FREEZER_PERIOD,
> > +};
> > +
> > +struct freezer_toggle {
> > + unsigned int enabled:1;
> > + unsigned int freeze_thaw:1; /* 1: freeze 0: thaw */
> > +} __packed;
> > +
> > +struct freezer_duty {
> > + u32 ratio; /* percentage of time frozen */
> > + u32 period_pct_ms; /* one percent of the period in
> > miliseconds */ +};
>
> I'd rather see you merge these two structures -- I don't see the value
> of keeping them separate nor of packing the struct. You could also
> merge the work item in there:
>
> struct freezer_duty {
> struct delayed_work freezer_work; /* work to duty-cycle a
> cgroup */
>
> u32 ratio; /* percentage of time frozen */
> u32 period_pct_ms; /* one percent of the period in
> miliseconds */ unsigned int enabled:1;
> unsigned int freeze_thaw:1; /* 1: freeze 0: thaw */
> };
>
> (I'm going to make the rest of my comments without assuming you've
> done this because it'll make them easier to follow given the context)
>
I don't have strong preference, but it seems more logical to merge all
toggling related structures. I will change that.
> > +
> > struct freezer {
> > struct cgroup_subsys_state css;
> > enum freezer_state state;
> > + struct freezer_duty duty;
> > + struct delayed_work freezer_work; /* work to duty-cycle a
> > cgroup */
> > + struct freezer_toggle toggle;
> > spinlock_t lock; /* protects _writes_ to state */
> > };
> >
> > +static int try_to_freeze_cgroup(struct cgroup *cgroup, struct
> > freezer *freezer); +static void unfreeze_cgroup(struct cgroup
> > *cgroup, struct freezer *freezer); +static int
> > freezer_change_state(struct cgroup *cgroup,
> > + enum freezer_state goal_state);
> > +
> > static inline struct freezer *cgroup_freezer(
> > struct cgroup *cgroup)
> > {
> > @@ -63,6 +87,41 @@ int cgroup_freezing_or_frozen(struct task_struct
> > *task) return result;
> > }
> >
> > +static DECLARE_WAIT_QUEUE_HEAD(freezer_wait);
> > +
> > +static void freezer_work_fn(struct work_struct *work)
> > +{
> > + struct freezer *freezer;
> > + unsigned long delay_jiffies = 0;
> > + enum freezer_state goal_state;
> > +
>
> Looking better. There are alot of field accesses here which can race
> with writes to the cgroup's duty ratio and period files. They should
> be protected. Perhaps we can reuse the freezer spin lock. That also
> has the benefit that we can eliminate the toggle.freeze_thaw bit I
> think:
>
I did think about the race, it does exist. but in practice. My thought
was that since freezer_change_state() holds the spin_lock of the
freezer, the race with writes to params are harmless, it just means the
new period or ratio will take effect in the next period.
In terms of using freezer spin lock to eliminate toggle flag, I am not
sure if i know how to do that. Are you suggesting based on whether the
spin lock is taken or not, we can decide the toggle? but the freeze
spin lock is used by other functions as well not just the delay work
here. I guess I have missed something.
> > +
> > + freezer = container_of(work, struct freezer,
> > freezer_work.work);
> > + /* toggle between THAWED and FROZEN state.
> > + * thaw if freezer->toggle.freeze_thaw = 0; freeze
> > otherwise
> > + * skip the first round if already in the target states.
> > + */
>
> spin_lock(&freezer->lock);
>
> > + if ((freezer->toggle.freeze_thaw && freezer->state ==
> > CGROUP_FROZEN) ||
> > + (!freezer->toggle.freeze_thaw &&
> > + freezer->state == CGROUP_THAWED)) {
> > + delay_jiffies = 0;
>
> This looks wrong. We should never schedule freezer work delayed by 0
> jiffies -- even if the delayed work API allows it. With 0-length
> delays I'd worry that we could peg the CPU in an obscure infinite
> loop.
>
> I think you can safely eliminate this block and the "exit_toggle"
> label.
>
Good point. My initial thought was that since the period for targeted
usage is quite long, e.g. 30 sec., we want to start the duty ratio
right away. But that shouldn't matter since we already schedule work
based on the new ratio/period.
> > + goto exit_toggle;
> > + } else if (freezer->toggle.freeze_thaw) {
>
> if (freezer->state == CGROUP_THAWED) {
>
> > + goal_state = CGROUP_FROZEN;
> > + delay_jiffies =
> > msecs_to_jiffies(freezer->duty.ratio *
> > +
> > freezer->duty.period_pct_ms);
> > + } else {
> > + goal_state = CGROUP_THAWED;
> > + delay_jiffies = msecs_to_jiffies((100 -
> > freezer->duty.ratio) *
> > +
> > freezer->duty.period_pct_ms);
> > + }
> > + freezer_change_state(freezer->css.cgroup, goal_state);
>
> __freezer_change_state(freezer->css.cgroup, goal_state);
> spin_unlock(&freezer->lock)
...
|
|
|
|
Current Time: Thu Aug 28 20:30:59 GMT 2025
Total time taken to generate the page: 0.09732 seconds
|
OpenVZ Forum
Members
Search
Help
Register
Login
Home
