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SubjectRe: [PATCH, v7] cgroups: introduce timer slack controller
On Wed, Mar 02, 2011 at 07:40:01PM +0100, Thomas Gleixner wrote:
> On Wed, 2 Mar 2011, Kirill A. Shutsemov wrote:
>
> Not CC'ing me does not avoid another review :)

Sorry for that. It's by mistake.

> > diff --git a/fs/select.c b/fs/select.c
> > index e56560d..a189e4d 100644
> > --- a/fs/select.c
> > +++ b/fs/select.c
> > @@ -69,7 +69,6 @@ static long __estimate_accuracy(struct timespec *tv)
> >
> > long select_estimate_accuracy(struct timespec *tv)
> > {
> > - unsigned long ret;
> > struct timespec now;
> >
> > /*
> > @@ -81,10 +80,8 @@ long select_estimate_accuracy(struct timespec *tv)
> >
> > ktime_get_ts(&now);
> > now = timespec_sub(*tv, now);
> > - ret = __estimate_accuracy(&now);
> > - if (ret < current->timer_slack_ns)
> > - return current->timer_slack_ns;
> > - return ret;
> > + return clamp(__estimate_accuracy(&now),
> > + get_task_timer_slack(current), LONG_MAX);
> > }
>
> Can you please split out the get_task_timer_slack() change into a
> separate patch?
>
> Also the function wants to be named different.
>
> task_get_effective_timer_slack() or such, so it becomes clear, that
> it's not just a wrapper around tsk->timer_slack_ns
>
> And the places which access tsk->timer_slack_ns directly should be
> updated with comments, why they are not using the wrapper.

Ok, I'll fix it.

> > +static int tslack_write_min(struct cgroup *cgroup, struct cftype *cft, u64 val)
> > +{
> > + struct cgroup *cur;
> > +
> > + if (val > ULONG_MAX)
> > + return -EINVAL;
> > +
> > + /* the min timer slack value should be more or equal than parent's */
>
> s/should/must/

Ok.

> > + if (cgroup->parent) {
> > + struct tslack_cgroup *parent = cgroup_to_tslack(cgroup->parent);
>
> New line between variables and code please

Ok.

> > + if (parent->min_slack_ns > val)
> > + return -EPERM;
> > + }
> > +
> > + cgroup_to_tslack(cgroup)->min_slack_ns = val;
> > +
> > + /* update children's min slack value if needed */
> > + list_for_each_entry(cur, &cgroup->children, sibling) {
> > + struct tslack_cgroup *child = cgroup_to_tslack(cur);
>
> Ditto
>
> > + if (val > child->min_slack_ns)
> > + tslack_write_min(cur, cft, val);
> > + }
>
> So, we can increase the value and propagate it through the groups
> children, but decreasing it requires to go through all child groups
> seperately.
>
> When I'm trying to optimize something during runtime and chose a too
> high value I need to go through hoops and loops to make it smaller
> again.
>
> Asymetric behaviour sucks always.

Other option is to remove restriction on the min_slack_ns value and
modify get_task_timer_slack() to use the most strict value up by
hierarchy.
Do you prefer this approach?

> > +unsigned long get_task_timer_slack(struct task_struct *tsk)
> > +{
> > + struct cgroup_subsys_state *css;
> > + struct tslack_cgroup *tslack_cgroup;
> > + unsigned long ret;
> > +
> > + rcu_read_lock();
>
> Did you just remove the odd comment or actually figure out why you
> need rcu_read_lock() here ?

The second ;)

> > + css = task_subsys_state(tsk, timer_slack_subsys.subsys_id);
> > + tslack_cgroup = container_of(css, struct tslack_cgroup, css);
> > + ret = max(tsk->timer_slack_ns, tslack_cgroup->min_slack_ns);
> > + rcu_read_unlock();
> > +
> > + return ret;
> > +}
>
> Otherwise, it's way more palatable than the last one.

Thanks for reviewing.

--
Kirill A. Shutemov


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