2022-11-23 06:14:23

by Kemeng Shi

Subject: [PATCH 09/11] blk-throttle: remove unnecessary check for validation of limit index

We always keep limit index valid as following:
Max limit is always valid and low limit can only be invalidated in
blk_throtl_update_limit_valid. Each time low limit may become invalid
after blk_throtl_update_limit_valid is called, we will check and make
sure current limit index is valid.

It's reasonable to always keep limit index valid, so we can remove this
check.

Signed-off-by: Kemeng Shi <[email protected]>
---
block/blk-throttle.c | 6 ++----
1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 3eccc7af4368..6f509cadd92b 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -418,12 +418,10 @@ static void tg_update_has_rules(struct throtl_grp *tg)
for (rw = READ; rw <= WRITE; rw++) {
tg->has_rules_iops[rw] =
(parent_tg && parent_tg->has_rules_iops[rw]) ||
- (td->limit_valid[td->limit_index] &&
- tg_iops_limit(tg, rw) != UINT_MAX);
+ (tg_iops_limit(tg, rw) != UINT_MAX);
tg->has_rules_bps[rw] =
(parent_tg && parent_tg->has_rules_bps[rw]) ||
- (td->limit_valid[td->limit_index] &&
- (tg_bps_limit(tg, rw) != U64_MAX));
+ (tg_bps_limit(tg, rw) != U64_MAX);
}
}

--
2.30.0

2022-11-23 19:20:29

by Tejun Heo

Subject: Re: [PATCH 09/11] blk-throttle: remove unnecessary check for validation of limit index

On Wed, Nov 23, 2022 at 02:03:59PM +0800, Kemeng Shi wrote:
> We always keep limit index valid as following:
> Max limit is always valid and low limit can only be invalidated in
> blk_throtl_update_limit_valid. Each time low limit may become invalid
> after blk_throtl_update_limit_valid is called, we will check and make
> sure current limit index is valid.
>
> It's reasonable to always keep limit index valid, so we can remove this
> check.

It's not obvious to me that it's correct and I'm not sure what we're gaining
by removing this while risking subtle breakages.

--
tejun

2022-11-24 13:49:12

by Kemeng Shi

Subject: Re: [PATCH 09/11] blk-throttle: remove unnecessary check for validation of limit index

on 11/24/2022 2:31 AM, Tejun Heo wrote:
> On Wed, Nov 23, 2022 at 02:03:59PM +0800, Kemeng Shi wrote:
>> We always keep limit index valid as following:
>> Max limit is always valid and low limit can only be invalidated in
>> blk_throtl_update_limit_valid. Each time low limit may become invalid
>> after blk_throtl_update_limit_valid is called, we will check and make
>> sure current limit index is valid.
>>
>> It's reasonable to always keep limit index valid, so we can remove this
>> check.
>
> It's not obvious to me that it's correct and I'm not sure what we're gaining
> by removing this while risking subtle breakages.
I will remove this patch in next version.

--
Best wishes
Kemeng Shi