[RFC PATCH] blk-mq: change bio_set_ioprio to inline

[RFC PATCH] blk-mq: change bio_set_ioprio to inline

[Liu Song]

From: Liu Song <liusong@linux.alibaba.com>

Change "bio_set_ioprio" to inline to avoid calling overhead.

Signed-off-by: Liu Song <liusong@linux.alibaba.com>
---
 block/blk-mq.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index c96c8c4..a17bc83 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2766,7 +2766,7 @@ static inline struct request *blk_mq_get_cached_request(struct request_queue *q,
 	return rq;
 }
 
-static void bio_set_ioprio(struct bio *bio)
+static inline void bio_set_ioprio(struct bio *bio)
 {
 	/* Nobody set ioprio so far? Initialize it based on task's nice value */
 	if (IOPRIO_PRIO_CLASS(bio->bi_ioprio) == IOPRIO_CLASS_NONE)
-- 
1.8.3.1

Re: [RFC PATCH] blk-mq: change bio_set_ioprio to inline

[Chaitanya Kulkarni]

On 8/30/22 02:45, Liu Song wrote:
> From: Liu Song <liusong@linux.alibaba.com>
> 
> Change "bio_set_ioprio" to inline to avoid calling overhead.
> 
> Signed-off-by: Liu Song <liusong@linux.alibaba.com>

for performance overhead please provide quantitative data

-ck

Re: [RFC PATCH] blk-mq: change bio_set_ioprio to inline

[Liu Song]

On 2022/8/30 20:48, Chaitanya Kulkarni wrote:

> On 8/30/22 02:45, Liu Song wrote:
>> From: Liu Song <liusong@linux.alibaba.com>
>>
>> Change "bio_set_ioprio" to inline to avoid calling overhead.
>>
>> Signed-off-by: Liu Song <liusong@linux.alibaba.com>
> for performance overhead please provide quantitative data
>
> -ck
>
This is a small adjustment, and even if performance comparison data is 
obtained
for targeted design use cases, it is not universal. If the inline by the 
compiler is
successful, the number of instructions will be reduced.

Thanks

>

Re: [RFC PATCH] blk-mq: change bio_set_ioprio to inline

[Jens Axboe]

On 8/30/22 3:45 AM, Liu Song wrote:
> From: Liu Song <liusong@linux.alibaba.com>
> 
> Change "bio_set_ioprio" to inline to avoid calling overhead.

Let's not try to 2nd guess the compiler here. Most things that are
marked inline should not be.

-- 
Jens Axboe

Re: [RFC PATCH] blk-mq: change bio_set_ioprio to inline

[Liu Song]

On 2022/8/30 21:59, Jens Axboe wrote:
> On 8/30/22 3:45 AM, Liu Song wrote:
>> From: Liu Song <liusong@linux.alibaba.com>
>>
>> Change "bio_set_ioprio" to inline to avoid calling overhead.
> Let's not try to 2nd guess the compiler here. Most things that are
> marked inline should not be.
Agree, I think there is something wrong with the commit log written here,
it should be expected to reduce the call overhead, bio_set_ioprio seems
to be appropriate to use inline.

Thanks

>

Re: [RFC PATCH] blk-mq: change bio_set_ioprio to inline

[Jens Axboe]

On 8/30/22 6:42 PM, Liu Song wrote:
> 
> On 2022/8/30 21:59, Jens Axboe wrote:
>> On 8/30/22 3:45 AM, Liu Song wrote:
>>> From: Liu Song <liusong@linux.alibaba.com>
>>>
>>> Change "bio_set_ioprio" to inline to avoid calling overhead.
>> Let's not try to 2nd guess the compiler here. Most things that are
>> marked inline should not be.
> Agree, I think there is something wrong with the commit log written here,
> it should be expected to reduce the call overhead, bio_set_ioprio seems
> to be appropriate to use inline.

I'm sure it's worth inlining, but did you check if it isn't already?
If it's small I'd fully expect the compiler to inline it already,
without needing to add things to do so.

-- 
Jens Axboe

Re: [RFC PATCH] blk-mq: change bio_set_ioprio to inline

[Liu Song]

On 2022/8/31 08:59, Jens Axboe wrote:
> On 8/30/22 6:42 PM, Liu Song wrote:
>> On 2022/8/30 21:59, Jens Axboe wrote:
>>> On 8/30/22 3:45 AM, Liu Song wrote:
>>>> From: Liu Song <liusong@linux.alibaba.com>
>>>>
>>>> Change "bio_set_ioprio" to inline to avoid calling overhead.
>>> Let's not try to 2nd guess the compiler here. Most things that are
>>> marked inline should not be.
>> Agree, I think there is something wrong with the commit log written here,
>> it should be expected to reduce the call overhead, bio_set_ioprio seems
>> to be appropriate to use inline.
> I'm sure it's worth inlining, but did you check if it isn't already?
> If it's small I'd fully expect the compiler to inline it already,
> without needing to add things to do so.
>
It is indeed possible, thanks for your reply.

Thanks