Messages in this thread | | | Subject | Re: [PATCH v6] sched: fix init NOHZ_IDLE flag | From | Peter Zijlstra <> | Date | Mon, 22 Apr 2013 11:30:52 +0200 |
| |
On Fri, 2013-04-19 at 15:10 +0200, Vincent Guittot wrote: > As suggested by Frederic Weisbecker, another solution is to have the > same > rcu lifecycle for both NOHZ_IDLE and sched_domain struct. I have > introduce > a new sched_domain_rq struct that is the entry point for both > sched_domains > and objects that must follow the same lifecycle like NOHZ_IDLE flags. > They > will share the same RCU lifecycle and will be always synchronized. > > The synchronization is done at the cost of : > - an additional indirection for accessing the first sched_domain > level > - an additional indirection and a rcu_dereference before accessing to > the > NOHZ_IDLE flag.
> diff --git a/include/linux/sched.h b/include/linux/sched.h > index d35d2b6..61ad5f1 100644 > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -959,6 +959,18 @@ struct sched_domain { > unsigned long span[0]; > }; > > +/* > + * Some flags must stay synchronized with fields of sched_group_power > and as a > + * consequence they must follow the same lifecycle for the lockless > scheme. > + * sched_domain_rq encapsulates those flags and sched_domains in one > RCU > + * object. > + */ > +struct sched_domain_rq { > + struct sched_domain *sd; > + unsigned long flags; > + struct rcu_head rcu; /* used during destruction */ > +};
I'm not quite getting things.. what's wrong with adding this flags thing to sched_domain itself? That's already RCU destroyed so why add a second RCU layer?
We also have the root_domain for things that don't need to go in a hierarchy but are once per cpu -- it sounds like this is one of those things; iirc the root_domain life-time is the same as the entire sched_domain tree so adding it to the root_domain is also an option.
| |