linux-kernel - Re: [LKP] Re: [btrfs] e076ab2a2c: fio.write

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Date:   Thu, 14 Jan 2021 23:50:28 +0100
From:   David Sterba <dsterba@...e.cz>
To:     Xing Zhengjun <zhengjun.xing@...ux.intel.com>
Cc:     dsterba@...e.cz, kernel test robot <oliver.sang@...el.com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        René Rebe <rene@...ctcode.de>,
        LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org,
        lkp@...el.com, ying.huang@...el.com, feng.tang@...el.com,
        linux-btrfs@...r.kernel.org
Subject: Re: [LKP] Re: [btrfs] e076ab2a2c: fio.write_iops -18.3% regression

On Wed, Jan 13, 2021 at 01:58:18PM +0800, Xing Zhengjun wrote:
> 
> 
> 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.

My plan is to find somebody who will fix it. Thanks.