block: add sysfs file for controlling io stats accounting

This allows us to turn off disk stat accounting completely, for the cases
where the 0.5-1% reduction in system time is important.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 28 insertions, 0 deletions

diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index b538ab8dbbd1..e29ddfc73cf4 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -197,6 +197,27 @@ queue_rq_affinity_store(struct request_queue *q, const char *page, size_t count)
         return ret;
 }
 
+static ssize_t queue_iostats_show(struct request_queue *q, char *page)
+{
+        return queue_var_show(blk_queue_io_stat(q), page);
+}
+
+static ssize_t queue_iostats_store(struct request_queue *q, const char *page,
+                                   size_t count)
+{
+        unsigned long stats;
+        ssize_t ret = queue_var_store(&stats, page, count);
+
+        spin_lock_irq(q->queue_lock);
+        if (stats)
+                queue_flag_set(QUEUE_FLAG_IO_STAT, q);
+        else
+                queue_flag_clear(QUEUE_FLAG_IO_STAT, q);
+        spin_unlock_irq(q->queue_lock);
+
+        return ret;
+}
+
 static struct queue_sysfs_entry queue_requests_entry = {
         .attr = {.name = "nr_requests", .mode = S_IRUGO | S_IWUSR },
         .show = queue_requests_show,
@@ -249,6 +270,12 @@ static struct queue_sysfs_entry queue_rq_affinity_entry = {
         .store = queue_rq_affinity_store,
 };
 
+static struct queue_sysfs_entry queue_iostats_entry = {
+        .attr = {.name = "iostats", .mode = S_IRUGO | S_IWUSR },
+        .show = queue_iostats_show,
+        .store = queue_iostats_store,
+};
+
 static struct attribute *default_attrs[] = {
         &queue_requests_entry.attr,
         &queue_ra_entry.attr,
@@ -259,6 +286,7 @@ static struct attribute *default_attrs[] = {
         &queue_nonrot_entry.attr,
         &queue_nomerges_entry.attr,
         &queue_rq_affinity_entry.attr,
+        &queue_iostats_entry.attr,
         NULL,
 };