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Subject: Re: [LKP] Re: [btrfs] e076ab2a2c: fio.write_iops -18.3% regression
To:     dsterba@suse.cz, kernel test robot <oliver.sang@intel.com>,
        Josef Bacik <josef@toxicpanda.com>,
        David Sterba <dsterba@suse.com>,
        =?UTF-8?Q?Ren=c3=a9_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,
        linux-btrfs@vger.kernel.org
References: <20210112153614.GA2015@xsang-OptiPlex-9020>
 <20210112154529.GT6430@twin.jikos.cz>
From:   Xing Zhengjun <zhengjun.xing@linux.intel.com>
Message-ID: <979aee28-c603-a187-e03f-29957c7b94d6@linux.intel.com>
Date:   Wed, 13 Jan 2021 13:58:18 +0800
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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