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Subject: Re: [f2fs-dev] [PATCH v4 2/2] f2fs: introduce periodic iostat io
 latency traces
To:     Daeho Jeong <daeho43@gmail.com>, linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com
Cc:     Daeho Jeong <daehojeong@google.com>
References: <20210820035229.216975-1-daeho43@gmail.com>
 <20210820035229.216975-2-daeho43@gmail.com>
From:   Chao Yu <chao@kernel.org>
Message-ID: <71203c35-4a9d-c43f-c74c-16a90bb5ff71@kernel.org>
Date:   Sat, 21 Aug 2021 05:52:49 +0800
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On 2021/8/20 11:52, Daeho Jeong wrote:
> From: Daeho Jeong <daehojeong@google.com>
> 
> Whenever we notice some sluggish issues on our machines, we are always
> curious about how well all types of I/O in the f2fs filesystem are
> handled. But, it's hard to get this kind of real data. First of all,
> we need to reproduce the issue while turning on the profiling tool like
> blktrace, but the issue doesn't happen again easily. Second, with the
> intervention of any tools, the overall timing of the issue will be
> slightly changed and it sometimes makes us hard to figure it out.
> 
> So, I added the feature printing out IO latency statistics tracepoint
> events, which are minimal things to understand filesystem's I/O related
> behaviors, into F2FS_IOSTAT kernel config. With "iostat_enable" sysfs
> node on, we can get this statistics info in a periodic way and it
> would cause the least overhead.
> 
> [samples]
>   f2fs_ckpt-254:1-507     [003] ....  2842.439683: f2fs_iostat_latency:
> dev = (254,11), iotype [peak lat.(ms)/avg lat.(ms)/count],
> rd_data [136/1/801], rd_node [136/1/1704], rd_meta [4/2/4],
> wr_sync_data [164/16/3331], wr_sync_node [152/3/648],
> wr_sync_meta [160/2/4243], wr_async_data [24/13/15],
> wr_async_node [0/0/0], wr_async_meta [0/0/0]
> 
>   f2fs_ckpt-254:1-507     [002] ....  2845.450514: f2fs_iostat_latency:
> dev = (254,11), iotype [peak lat.(ms)/avg lat.(ms)/count],
> rd_data [60/3/456], rd_node [60/3/1258], rd_meta [0/0/1],
> wr_sync_data [120/12/2285], wr_sync_node [88/5/428],
> wr_sync_meta [52/6/2990], wr_async_data [4/1/3],
> wr_async_node [0/0/0], wr_async_meta [0/0/0]
> 
> ---
> v4: separate the previous patch into two patches
> v3: moved other I/O statistics related features into a separate file
>      with the same kernel config option for better maintenance.
> v2: clean up with wrappers and fix a build breakage reported by
>      kernel test robot <lkp@intel.com>
> 
> Signed-off-by: Daeho Jeong <daehojeong@google.com>

It needs to move Signed-off-by tag to the front of change log section,
otherwise it will be missed during applying.

Thanks,