[dm-devel] Re: [PATCH 07/20] io-controller: Export disk time used and nr sectors dipatched through cgroups

[Gui Jianfeng]

Vivek Goyal wrote:
...
> +
> +static int io_cgroup_disk_sectors_read(struct cgroup *cgroup,
> +				struct cftype *cftype, struct seq_file *m)
> +{
> +	struct io_cgroup *iocg;
> +	struct io_group *iog;
> +	struct hlist_node *n;
> +
> +	if (!cgroup_lock_live_group(cgroup))
> +		return -ENODEV;
> +
> +	iocg = cgroup_to_io_cgroup(cgroup);
> +
> +	spin_lock_irq(&iocg->lock);

It's better to make use of rcu_read_lock instead since it's
a read action.

Signed-off-by: Gui Jianfeng <guijianfeng at cn.fujitsu.com>
---
 block/elevator-fq.c |   12 ++++++------
 1 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/block/elevator-fq.c b/block/elevator-fq.c
index 2ad40eb..d779282 100644
--- a/block/elevator-fq.c
+++ b/block/elevator-fq.c
@@ -1418,7 +1418,7 @@ static int io_cgroup_disk_time_read(struct cgroup *cgroup,
 
 	iocg = cgroup_to_io_cgroup(cgroup);
 
-	spin_lock_irq(&iocg->lock);
+	rcu_read_lock();
 	hlist_for_each_entry_rcu(iog, n, &iocg->group_data, group_node) {
 		/*
 		 * There might be groups which are not functional and
@@ -1430,7 +1430,7 @@ static int io_cgroup_disk_time_read(struct cgroup *cgroup,
 					iog->entity.total_service);
 		}
 	}
-	spin_unlock_irq(&iocg->lock);
+	rcu_read_unlock();
 	cgroup_unlock();
 
 	return 0;
@@ -1448,7 +1448,7 @@ static int io_cgroup_disk_sectors_read(struct cgroup *cgroup,
 
 	iocg = cgroup_to_io_cgroup(cgroup);
 
-	spin_lock_irq(&iocg->lock);
+	rcu_read_lock();
 	hlist_for_each_entry_rcu(iog, n, &iocg->group_data, group_node) {
 		/*
 		 * There might be groups which are not functional and
@@ -1460,7 +1460,7 @@ static int io_cgroup_disk_sectors_read(struct cgroup *cgroup,
 					iog->entity.total_sector_service);
 		}
 	}
-	spin_unlock_irq(&iocg->lock);
+	rcu_read_unlock();
 	cgroup_unlock();
 
 	return 0;
@@ -1478,7 +1478,7 @@ static int io_cgroup_disk_queue_read(struct cgroup *cgroup,
 		return -ENODEV;
 
 	iocg = cgroup_to_io_cgroup(cgroup);
-	spin_lock_irq(&iocg->lock);
+	rcu_read_lock();
 	/* Loop through all the io groups and print statistics */
 	hlist_for_each_entry_rcu(iog, n, &iocg->group_data, group_node) {
 		/*
@@ -1491,7 +1491,7 @@ static int io_cgroup_disk_queue_read(struct cgroup *cgroup,
 					iog->queue_duration);
 		}
 	}
-	spin_unlock_irq(&iocg->lock);
+	rcu_read_unlock();
 	cgroup_unlock();
 
 	return 0;
-- 
1.5.4.rc3



> +	hlist_for_each_entry_rcu(iog, n, &iocg->group_data, group_node) {
> +		/*
> +		 * There might be groups which are not functional and
> +		 * waiting to be reclaimed upon cgoup deletion.
> +		 */
> +		if (iog->key) {
> +			seq_printf(m, "%u %u %lu\n", MAJOR(iog->dev),
> +					MINOR(iog->dev),
> +					iog->entity.total_sector_service);
> +		}
> +	}
> +	spin_unlock_irq(&iocg->lock);
> +	cgroup_unlock();
> +
> +	return 0;
> +}
> +
>