Messages in this thread | | | Date | Fri, 17 Feb 2012 09:14:28 -0800 | From | Tejun Heo <> | Subject | Re: [PATCH 2/9] blkcg: drop unnecessary RCU locking |
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On Fri, Feb 17, 2012 at 09:07:13AM -0800, Tejun Heo wrote: > On Fri, Feb 17, 2012 at 11:19:58AM -0500, Vivek Goyal wrote: > > On Thu, Feb 16, 2012 at 02:37:51PM -0800, Tejun Heo wrote: > > > Now that blkg additions / removals are always done under both q and > > > blkcg locks, the only place RCU locking is used is blkg_lookup() for > > > lockless lookup. This patch drops unncessary RCU locking replacing it > > > with plain blkcg / q locking as necessary. > > > > > > * blkg_lookup_create() and blkiocg_pre_destroy() already perform > > > proper locking and don't need RCU. Dropped. > > > > But blkg_lookup_create() is called under rcu() to protect blkcg pointer. > > And blkg_lookup() is also happening under same rcu read lock. So I think > > you can't drop rcu from blkg_lookup_create(). > > Ooh, right. Will fix.
BTW, the reason this doesn't work is due to the broken percpu allocation in blkg_alloc(). We should remove unnecessary rcu lockings after updating stat allocation.
Thanks.
-- tejun
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