On Wed, Jan 23 2008, Andrew Morton wrote: > > On Tue, 22 Jan 2008 10:49:19 +0100 Jens Axboe <[EMAIL PROTECTED]> wrote: > > The io context sharing introduced a per-ioc spinlock, that would protect > > the cfq io context lookup. That is a regression from the original, since > > we never needed any locking there because the ioc/cic were process private. > > > > The cic lookup is changed from an rbtree construct to a radix tree, which > > we can then use RCU to make the reader side lockless. That is the > > performance > > critical path, modifying the radix tree is only done on process creation > > (when that process first does IO, actually) and on process exit (if that > > process has done IO). > > Perhaps Paul would review the rcu usage here sometime?
That would indeed be awesome :-) > > +/* > > + * Add cic into ioc, using cfqd as the search key. This enables us to > > lookup > > + * the process specific cfq io context when entered from the block layer. > > + * Also adds the cic to a per-cfqd list, used when this queue is removed. > > + */ > > +static inline int > > There's a lot of pointless inlining in there. Will kill. > > +++ b/block/ll_rw_blk.c > > @@ -3831,6 +3831,16 @@ int __init blk_dev_init(void) > > return 0; > > } > > > > +static void cfq_dtor(struct io_context *ioc) > > +{ > > + struct cfq_io_context *cic[1]; > > + int r; > > + > > + r = radix_tree_gang_lookup(&ioc->radix_root, (void **) cic, 0, 1); > > + if (r > 0) > > + cic[0]->dtor(ioc); > > +} > > Some comments here might help others who are wondering why we can't just > use radix_tree_lookup(). Sure, will add a comment. > > @@ -3900,7 +3911,7 @@ struct io_context *alloc_io_context(gfp_t gfp_flags, > > int node) > > ret->last_waited = jiffies; /* doesn't matter... */ > > ret->nr_batch_requests = 0; /* because this is 0 */ > > ret->aic = NULL; > > - ret->cic_root.rb_node = NULL; > > + INIT_RADIX_TREE(&ret->radix_root, GFP_ATOMIC | __GFP_HIGH); > > Did this need to be atomic? It's actually only ever used with a radix_tree_preload() where the proper gfp mask is passed, the actual radix_tree_insert() is done under lock protecting the tree. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/