On Tue, Jan 12, 2021 at 11:36:14PM +0800, kernel test robot wrote:
>
> Greeting,
>
> FYI, we noticed a -18.3% regression of fio.write_iops due to commit:
>
>
> commit: e076ab2a2ca70a0270232067cd49f76cd92efe64 ("btrfs: shrink delalloc
> pages instead of full inodes")
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
>
>
> in testcase: fio-basic
> on test machine: 192 threads Intel(R) Xeon(R) CPU @ 2.20GHz with 192G memory
> with following parameters:
>
> disk: 1SSD
> fs: btrfs
> runtime: 300s
> nr_task: 8
> rw: randwrite
> bs: 4k
> ioengine: sync
> test_size: 256g
Though I do a similar test (emulating bit torrent workload), it's a bit
extreme as it's 4k synchronous on a huge file. It always takes a lot of
time but could point out some concurrency issues namely on faster
devices. There are 8 threads possibly competing for the same inode lock
or other locks related to it.
The mentioned commit fixed another perf regression on a much more common
workload (untgrring files), so at this point drop in this fio workload
is inevitable.
