[rh8,2/2] ms/block, bfq: add weight symlink to the bfq.weight cgroup parameter

Submitted by Andrey Ryabinin on Jan. 24, 2020, 4:10 p.m.

Details

Message ID 20200124161012.29948-2-aryabinin@virtuozzo.com
State New
Series "Series without cover letter"
Headers show

Commit Message

Andrey Ryabinin Jan. 24, 2020, 4:10 p.m.
From: Angelo Ruocco <angeloruocco90@gmail.com>

Many userspace tools and services use the proportional-share policy of
the blkio/io cgroups controller. The CFQ I/O scheduler implemented
this policy for the legacy block layer. To modify the weight of a
group in case CFQ was in charge, the 'weight' parameter of the group
must be modified. On the other hand, the BFQ I/O scheduler implements
the same policy in blk-mq, but, with BFQ, the parameter to modify has
a different name: bfq.weight (forced choice until legacy block was
present, because two different policies cannot share a common parameter
in cgroups).

Due to CFQ legacy, most if not all userspace configurations still use
the parameter 'weight', and for the moment do not seem likely to be
changed. But, when CFQ went away with legacy block, such a parameter
ceased to exist.

So, a simple workaround has been proposed [1] to make all
configurations work: add a symlink, named weight, to bfq.weight. This
commit adds such a symlink.

[1] https://lkml.org/lkml/2019/4/8/555

Suggested-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Angelo Ruocco <angeloruocco90@gmail.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

(cherry-picked from 19e9da9e86c43687ed6a56bd39a52c6649973a35)
https://jira.sw.ru/browse/PSBM-101019
Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>
---
 block/bfq-cgroup.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Patch hide | download patch | download mbox

diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index c6113af31960..27f158f2ef2c 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -1054,7 +1054,8 @@  struct blkcg_policy blkcg_policy_bfq = {
 struct cftype bfq_blkcg_legacy_files[] = {
 	{
 		.name = "bfq.weight",
-		.flags = CFTYPE_NOT_ON_ROOT,
+		.link_name = "weight",
+		.flags = CFTYPE_NOT_ON_ROOT | CFTYPE_SYMLINKED,
 		.seq_show = bfq_io_show_weight,
 		.write_u64 = bfq_io_set_weight_legacy,
 	},
@@ -1174,7 +1175,8 @@  struct cftype bfq_blkcg_legacy_files[] = {
 struct cftype bfq_blkg_files[] = {
 	{
 		.name = "bfq.weight",
-		.flags = CFTYPE_NOT_ON_ROOT,
+		.link_name = "weight",
+		.flags = CFTYPE_NOT_ON_ROOT | CFTYPE_SYMLINKED,
 		.seq_show = bfq_io_show_weight,
 		.write = bfq_io_set_weight,
 	},