[PATCH] cfq-iosched: use new io context counting mechanism

It's ok if the read path is a lot more costly, as long as inc/dec is
really cheap. The inc/dec will happen for each created/freed io context,
while the reading only happens when a disk queue exits.

Signed-off-by: Jens Axboe <axboe@suse.de>

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 33e0b0c..c988aa7 100644 (file)
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -46,7 +46,7 @@ static int cfq_slice_idle = HZ / 125;
 static kmem_cache_t *cfq_pool;
 static kmem_cache_t *cfq_ioc_pool;
 
-static atomic_t ioc_count = ATOMIC_INIT(0);
+static DEFINE_PER_CPU(unsigned long, ioc_count);
 static struct completion *ioc_gone;
 
 #define CFQ_PRIO_LISTS         IOPRIO_BE_NR
@@ -1078,7 +1078,9 @@ static void cfq_free_io_context(struct io_context *ioc)
                freed++;
        }
 
-       if (atomic_sub_and_test(freed, &ioc_count) && ioc_gone)
+       elv_ioc_count_mod(ioc_count, -freed);
+
+       if (ioc_gone && !elv_ioc_count_read(ioc_count))
                complete(ioc_gone);
 }
 
@@ -1154,7 +1156,7 @@ cfq_alloc_io_context(struct cfq_data *cfqd, gfp_t gfp_mask)
                INIT_LIST_HEAD(&cic->queue_list);
                cic->dtor = cfq_free_io_context;
                cic->exit = cfq_exit_io_context;
-               atomic_inc(&ioc_count);
+               elv_ioc_count_inc(ioc_count);
        }
 
        return cic;
@@ -1319,7 +1321,7 @@ cfq_drop_dead_cic(struct io_context *ioc, struct cfq_io_context *cic)
        WARN_ON(!list_empty(&cic->queue_list));
        rb_erase(&cic->rb_node, &ioc->cic_root);
        kmem_cache_free(cfq_ioc_pool, cic);
-       atomic_dec(&ioc_count);
+       elv_ioc_count_dec(ioc_count);
 }
 
 static struct cfq_io_context *
@@ -2165,7 +2167,7 @@ static void __exit cfq_exit(void)
        ioc_gone = &all_gone;
        /* ioc_gone's update must be visible before reading ioc_count */
        smp_wmb();
-       if (atomic_read(&ioc_count))
+       if (elv_ioc_count_read(ioc_count))
                wait_for_completion(ioc_gone);
        synchronize_rcu();
        cfq_slab_kill();