Re: [LKP] Re: [btrfs] e076ab2a2c: fio.write_iops -18.3% regression

[Xing Zhengjun]

On 1/12/2021 11:45 PM, David Sterba wrote:
> 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.

Do you have a plan to fix it? Thanks.
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--
Zhengjun Xing