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authorTejun Heo <tj@kernel.org>2023-04-12 14:06:49 -1000
committerJens Axboe <axboe@kernel.dk>2023-04-13 06:46:49 -0600
commita13696b83da4f1e53e192ec3e239afd3a96ff747 (patch)
treea54ab31b1a940a496760bdc0c0c62b7394b0bf2e /block/blk-iolatency.c
parent3304918758125a0eb18fb480c82945e327b81f78 (diff)
blk-iolatency: Make initialization lazy
Other rq_qos policies such as wbt and iocost are lazy-initialized when they are configured for the first time for the device but iolatency is initialized unconditionally from blkcg_init_disk() during gendisk init. Lazy init is beneficial because rq_qos policies add runtime overhead when initialized as every IO has to walk all registered rq_qos callbacks. This patch switches iolatency to lazy initialization too so that it only registered its rq_qos policy when it is first configured. Note that there is a known race condition between blkcg config file writes and del_gendisk() and this patch makes iolatency susceptible to it by exposing the init path to race against the deletion path. However, that problem already exists in iocost and is being worked on. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Christoph Hellwig <hch@lst.de> Cc: Josef Bacik <josef@toxicpanda.com> Link: https://lore.kernel.org/r/20230413000649.115785-5-tj@kernel.org Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/blk-iolatency.c')
-rw-r--r--block/blk-iolatency.c29
1 files changed, 28 insertions, 1 deletions
diff --git a/block/blk-iolatency.c b/block/blk-iolatency.c
index 2560708b9109..fd5fec989e39 100644
--- a/block/blk-iolatency.c
+++ b/block/blk-iolatency.c
@@ -755,7 +755,7 @@ static void blkiolatency_enable_work_fn(struct work_struct *work)
}
}
-int blk_iolatency_init(struct gendisk *disk)
+static int blk_iolatency_init(struct gendisk *disk)
{
struct blk_iolatency *blkiolat;
int ret;
@@ -824,6 +824,29 @@ static void iolatency_clear_scaling(struct blkcg_gq *blkg)
}
}
+static int blk_iolatency_try_init(struct blkg_conf_ctx *ctx)
+{
+ static DEFINE_MUTEX(init_mutex);
+ int ret;
+
+ ret = blkg_conf_open_bdev(ctx);
+ if (ret)
+ return ret;
+
+ /*
+ * blk_iolatency_init() may fail after rq_qos_add() succeeds which can
+ * confuse iolat_rq_qos() test. Make the test and init atomic.
+ */
+ mutex_lock(&init_mutex);
+
+ if (!iolat_rq_qos(ctx->bdev->bd_queue))
+ ret = blk_iolatency_init(ctx->bdev->bd_disk);
+
+ mutex_unlock(&init_mutex);
+
+ return ret;
+}
+
static ssize_t iolatency_set_limit(struct kernfs_open_file *of, char *buf,
size_t nbytes, loff_t off)
{
@@ -838,6 +861,10 @@ static ssize_t iolatency_set_limit(struct kernfs_open_file *of, char *buf,
blkg_conf_init(&ctx, buf);
+ ret = blk_iolatency_try_init(&ctx);
+ if (ret)
+ goto out;
+
ret = blkg_conf_prep(blkcg, &blkcg_policy_iolatency, &ctx);
if (ret)
goto out;