Hi Paul, Joel, > > > On the other hand, would you have ideas for more modern replacement > > > examples? > > > > There are 3 cases I can see in listRCU.txt: > > (1) action taken outside of read_lock (can tolerate stale data), no in-place update. > > this is the best possible usage of RCU. > > (2) action taken outside of read_lock, in-place updates > > this is good as long as not too many in-place updates. > > involves copying creating new list node and replacing the > > node being updated with it. > > (3) cannot tolerate stale data: here a deleted or obsolete flag can be used > > protected by a per-entry lock. reader > > aborts if object is stale. > > > > Any replacement example must make satisfy (3) too? > > It would be OK to have a separate example for (3). It would of course > be nicer to have one example for all three, but not all -that- important. > > > The only example for (3) that I know of is sysvipc sempahores which you also > > mentioned in the paper. Looking through this code, it hasn't changed > > conceptually and it could be a fit for an example (ipc_valid_object() checks > > for whether the object is stale). > > That is indeed the classic canonical example. ;-) > > > The other example could be dentry look up which uses seqlocks for the > > RCU-walk case? But that could be too complex. This is also something I first > > learnt from the paper and then the excellent path-lookup.rst document in > > kernel sources. > > This is a great example, but it would need serious simplification for > use in the Documentation/RCU directory. Note that dcache uses it to > gain very limited and targeted consistency -- only a few types of updates > acquire the write-side of that seqlock. > > Might be quite worthwhile to have a simplified example, though! > Perhaps a trivial hash table where write-side sequence lock is acquired > only when moving an element from one chain to another? Sorry to take you down here..., but what do you mean by "the paper"? ;-/ Thanx, Andrea
