Messages in this thread | | | Date | Fri, 3 Mar 2017 09:17:37 +0900 | From | Byungchul Park <> | Subject | Re: [PATCH v5 06/13] lockdep: Implement crossrelease feature |
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On Thu, Mar 02, 2017 at 02:40:31PM +0100, Peter Zijlstra wrote: > On Wed, Mar 01, 2017 at 01:28:43PM +0100, Peter Zijlstra wrote: > > On Wed, Mar 01, 2017 at 02:43:23PM +0900, Byungchul Park wrote: > > > > It's an optimization, but very essential and important optimization. > > Since its not for correctness, please put it in a separate patch with a > good Changelog, the below would make a good beginning of that.
OK. I will do it.
> Also, I feel, the source comments can be improved. > > > > in hlocks[] > > > ------------ > > > A gen_id (4) --+ > > > | previous gen_id > > > B gen_id (3) <-+ > > > C gen_id (3) > > > D gen_id (2) > > > oldest -> E gen_id (1) > > > > > > in xhlocks[] > > > ------------ > > > ^ A gen_id (4) prev_gen_id (3: B's gen id) > > > | B gen_id (3) prev_gen_id (3: C's gen id) > > > | C gen_id (3) prev_gen_id (2: D's gen id) > > > | D gen_id (2) prev_gen_id (1: E's gen id) > > > | E gen_id (1) prev_gen_id (NA) > > > > > > Let's consider the case that the gen id of xlock to commit is 3. > > > > > > In this case, it's engough to generate 'the xlock -> C'. 'the xlock -> B' > > > and 'the xlock -> A' are unnecessary since it's covered by 'C -> B' and > > > 'B -> A' which are already generated by original lockdep. > > > > > > I use the prev_gen_id to avoid adding this kind of redundant > > > dependencies. In other words, xhlock->prev_gen_id >= xlock->hlock.gen_id > > > means that the previous lock in hlocks[] is able to handle the > > > dependency on its commit stage.
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c > index a95e5d1..7baea89 100644 > --- a/kernel/locking/lockdep.c > +++ b/kernel/locking/lockdep.c > @@ -1860,6 +1860,17 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev, > } > } > > + /* > + * Is the <prev> -> <next> redundant? > + */ > + this.class = hlock_class(prev); > + this.parent = NULL; > + ret = check_noncircular(&this, hlock_class(next), &target_entry); > + if (!ret) /* exists, redundant */ > + return 2; > + if (ret < 0) > + return print_bfs_bug(ret); > + > if (!*stack_saved) { > if (!save_trace(&trace)) > return 0;
This whoud be very nice if you allow to add this code. However, prev_gen_id thingy is still useful, the code above can achieve it though. Agree?
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