On Fri, Jun 07, 2019 at 06:29:48PM +0206, John Ogness wrote: > +/** > + * DOC: memory barriers
What's up with that 'DOC' crap? > + * > + * Writers > + * ------- > + * The main issue with writers is expiring/invalidating old data blocks in > + * order to create new data blocks. This is performed in 6 steps that must > + * be observed in order by all writers to allow cooperation. Here is a list > + * of the 6 steps and the named acquire/release memory barrier pairs that > + * are used to synchronized them: > + * > + * * old data invalidation (MB1): Pushing rb.data_list.oldest forward. > + * Necessary for identifying if data has been expired. > + * > + * * new data reservation (MB2): Pushing rb.data_list.newest forward. > + * Necessary for validating data. > + * > + * * assign the data block to a descriptor (MB3): Setting data block id to > + * descriptor id. Necessary for finding the descriptor associated with th > + * data block. > + * > + * * commit data (MB4): Setting data block data_next. (Now data block is > + * valid). Necessary for validating data. > + * > + * * make descriptor newest (MB5): Setting rb.descr_list.newest to > descriptor. > + * (Now following new descriptors will be linked to this one.) Necessary > for > + * ensuring the descriptor's next is set to EOL before adding to the list. > + * > + * * link descriprtor to previous newest (MB6): Setting the next of the > + * previous descriptor to this one. Necessary for correctly identifying if > + * a descriptor is the only descriptor on the list. > + * > + * Readers > + * ------- > + * Readers only make of smb_rmb() to ensure that certain critical load > + * operations are performed in an order that allows readers to evaluate if > + * the data they read is really valid. > + */ This isn't really helping much I feel. It doesn't begin to describe the ordering. But maybe the code makes more sense.
