Re: [PATCH v3] blk-throtl: optimize IOPS throttle for large IO scenarios

Date: Sat Aug 14 2021 - 19:53:20 EST

Hi Jens:

Should we apply this patch for new and older kernel ?


On 2021/8/10 6:39 AM, Tejun Heo wrote:
On Mon, Aug 02, 2021 at 11:51:56AM +0800, brookxu wrote:
From: Chunguang Xu <brookxu@xxxxxxxxxxx>

After patch 54efd50 (block: make generic_make_request handle
arbitrarily sized bios), the IO through io-throttle may be larger,
and these IOs may be further split into more small IOs. However,
IOPS throttle does not seem to be aware of this change, which
makes the calculation of IOPS of large IOs incomplete, resulting
in disk-side IOPS that does not meet expectations. Maybe we should
fix this problem.

We can reproduce it by set max_sectors_kb of disk to 128, set
blkio.write_iops_throttle to 100, run a dd instance inside blkio
and use iostat to watch IOPS:

dd if=/dev/zero of=/dev/sdb bs=1M count=1000 oflag=direct

As a result, without this change the average IOPS is 1995, with
this change the IOPS is 98.

v3: Optimize the use of atomic variables.
v2: Use atomic variables to solve synchronization problems.

Signed-off-by: Chunguang Xu <brookxu@xxxxxxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>