> 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?
> +/*
> + * 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.
> +++ 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().
> +static void cfq_exit(struct io_context *ioc)
> +{
> + struct cfq_io_context *cic[1];
> + int r;
> +
> + rcu_read_lock();
> + r = radix_tree_gang_lookup(&ioc->radix_root, (void **) cic, 0, 1);
> + rcu_read_unlock();
> +
> + if (r > 0)
> + cic[0]->exit(ioc);
> +}
ditto.
> /* Called by the exitting task */
> void exit_io_context(void)
> {
> struct io_context *ioc;
> - struct cfq_io_context *cic;
>
> task_lock(current);
> ioc = current->io_context;
> @@ -3876,11 +3891,7 @@ void exit_io_context(void)
> if (atomic_dec_and_test(&ioc->nr_tasks)) {
> if (ioc->aic && ioc->aic->exit)
> ioc->aic->exit(ioc->aic);
> - if (ioc->cic_root.rb_node != NULL) {
> - cic = rb_entry(rb_first(&ioc->cic_root),
> - struct cfq_io_context, rb_node);
> - cic->exit(ioc);
> - }
> + cfq_exit(ioc);
>
> put_io_context(ioc);
> }
> @@ -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?
--
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/
