Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Tue, 12 Jan 2021 16:45:29 +0100
From:   David Sterba <dsterba@suse.cz>
To:     kernel test robot <oliver.sang@intel.com>
Cc:     Josef Bacik <josef@toxicpanda.com>,
        David Sterba <dsterba@suse.com>,
        =?iso-8859-1?Q?Ren=E9?= Rebe <rene@exactcode.de>,
        LKML <linux-kernel@vger.kernel.org>, lkp@lists.01.org,
        lkp@intel.com, ying.huang@intel.com, feng.tang@intel.com,
        zhengjun.xing@intel.com, linux-btrfs@vger.kernel.org
Subject: Re: [btrfs]  e076ab2a2c:  fio.write_iops -18.3% regression
Message-ID: <20210112154529.GT6430@twin.jikos.cz>
Reply-To: dsterba@suse.cz
Mail-Followup-To: dsterba@suse.cz,
        kernel test robot <oliver.sang@intel.com>,
        Josef Bacik <josef@toxicpanda.com>, David Sterba <dsterba@suse.com>,
        =?iso-8859-1?Q?Ren=E9?= Rebe <rene@exactcode.de>,
        LKML <linux-kernel@vger.kernel.org>, lkp@lists.01.org,
        lkp@intel.com, ying.huang@intel.com, feng.tang@intel.com,
        zhengjun.xing@intel.com, linux-btrfs@vger.kernel.org
References: <20210112153614.GA2015@xsang-OptiPlex-9020>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20210112153614.GA2015@xsang-OptiPlex-9020>
User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12)
Precedence: bulk

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.