Messages in this thread | | | Subject | Re: [PATCH 11/13] hrtimer: turn hrtimers into range timers | From | Peter Zijlstra <> | Date | Tue, 02 Sep 2008 13:08:45 +0200 |
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On Tue, 2008-09-02 at 10:22 +0200, Peter Zijlstra wrote: > On Mon, 2008-09-01 at 16:08 -0700, Arjan van de Ven wrote: > > > @@ -847,7 +847,8 @@ static void enqueue_hrtimer(struct hrtimer *timer, > > * We dont care about collisions. Nodes with > > * the same expiry time stay together. > > */ > > - if (timer->expires.tv64 < entry->expires.tv64) { > > + if (hrtimer_get_expires_tv64(timer) < > > + hrtimer_get_expires_tv64(entry)) { > > link = &(*link)->rb_left; > > } else { > > link = &(*link)->rb_right; > > On Mon, 2008-09-01 at 16:13 -0700, Arjan van de Ven wrote: > > > +static inline void hrtimer_set_expires_range(struct hrtimer *timer, ktime_t time, ktime_t delta) > > +{ > > + timer->_softexpires = time; > > + timer->_expires = ktime_add_safe(time, delta); > > +} > > > @@ -241,10 +259,19 @@ static inline ktime_t hrtimer_get_expires(const struct hrtimer *timer) > > return timer->_expires; > > } > > > > +static inline ktime_t hrtimer_get_softexpires(const struct hrtimer *timer) > > +{ > > + return timer->_expires; > > +} > > Somehow the function is called softexpires, but returns the hard expire > time... > > > static inline s64 hrtimer_get_expires_tv64(const struct hrtimer *timer) > > { > > return timer->_expires.tv64; > > } > > +static inline s64 hrtimer_get_softexpires_tv64(const struct hrtimer *timer) > > +{ > > + return timer->_softexpires.tv64; > > +} > > > > static inline s64 hrtimer_get_expires_ns(const struct hrtimer *timer) > > { > > > @@ -1309,7 +1309,7 @@ void hrtimer_interrupt(struct clock_event_device *dev) > > > > timer = rb_entry(node, struct hrtimer, node); > > > > - if (basenow.tv64 < hrtimer_get_expires_tv64(timer)) { > > + if (basenow.tv64 < hrtimer_get_softexpires_tv64(timer)) { > > ktime_t expires; > > > > expires = ktime_sub(hrtimer_get_expires(timer), > > I might be missing something, but this code only looks at the leftmost > timer, and we're indexed on the hard expire time, which might be rather > far to the right of here. > > This means that esp for those timers for which we can save most we're > least likely to do so because we'll plain not see them.
What you need is a data structure that supports stabbing queries on overlapping intervals, such like a Priority Search Tree.
If I'm not mistaken, then the augmented Red-Black tree from the EEVDF paper is identical to PST [*].
This data-structure adds a Heap property to each RB-node, allowing one to search the tree on a different property.
So what you can do in this case, is index the RB-tree on the soft expire, and index the heap on the hard expire.
Then you can find the leftmost hard expire by traversing the tree using the heap property - and program the clock-event using that time.
And you can search for soft expired entries using the RB-tree like we do now.
[*] Fabio implemented it on top of the linux RB-tree for their wf2q+ implementation that they used for their BFQ I/O scheduler:
http://feanor.sssup.it/~fabio/linux/wfq/
And I borrowed their implementation for my scheduler work:
http://programming.kicks-ass.net/kernel-patches/sched-eevdf/sched-eedf.patch
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