Re: [PATCH] block: throttle: charge io re-submission for iops limit

[Ming Lei <ming.lei@redhat.com>]

On Thu, Jan 06, 2022 at 03:46:54PM +0800, brookxu wrote:
> Hi Ming:
> 
> I think it may be due to other reasons, I test this patch seems work fine,
> Can you verify it in your environment?

Your patch can't cover the issue Ning Li reported.

> 
> 
> From 2c7305042e71d0f53ca50a8a3f2eebe6a2dcdb86 Mon Sep 17 00:00:00 2001
> From: Chunguang Xu <brookxu@tencent.com>
> Date: Thu, 6 Jan 2022 15:18:50 +0800
> Subject: [PATCH] blk-throtl: avoid double charge of bio IOPS due to split
> 
> After commit 900e08075202("block: move queue enter logic into
> blk_mq_submit_bio()"), submit_bio_checks() is moved from the
> entrance of the IO stack to the specific submit_bio() entrance.
> Therefore, the IO may be splited before entering blk-throtl, so
> we need to check whether the BIO is throttled, and only need
> to update the io_split_cnt for the throttled bio to avoid
> double charge.

Actually since commit 900e08075202, your commit 4f1e9630afe6
("blk-throtl: optimize IOPS throttle for large IO scenarios") doesn't
need any more, because split bio is always sent to submit_bio_checks().

But I don't think that way is reasonable, especially precise driver tag
and request is consumed by each throttling, so the following patch is posted:

https://lore.kernel.org/linux-block/20220104134223.590803-1-ming.lei@redhat.com/T/#u


Thanks,
Ming