linux-kernel - Re: [f2fs-dev] [PATCH v2] f2fs: introduce periodic iostat io latency traces

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Date:   Fri, 13 Aug 2021 09:14:00 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     Daeho Jeong <daeho43@...il.com>, linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, kernel-team@...roid.com,
        Daeho Jeong <daehojeong@...gle.com>
Subject: Re: [f2fs-dev] [PATCH v2] f2fs: introduce periodic iostat io latency
 traces

On 2021/8/13 4:52, Jaegeuk Kim wrote:
> On 08/11, Chao Yu wrote:
>> Hi Daeho,
>>
>> On 2021/8/4 6:55, Daeho Jeong wrote:
>>> From: Daeho Jeong <daehojeong@...gle.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 F2FS_IOSTAT_IO_LATENCY config option to support printing out
>>> IO latency statistics tracepoint events which are minimal things to
>>> understand filesystem's I/O related behaviors. 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]
>>>
>>> Signed-off-by: Daeho Jeong <daehojeong@...gle.com>
>>>
>>> ---
>>> v2: clean up with wrappers and fix a build breakage reported by
>>>       kernel test robot <lkp@...el.com>
>>> ---
>>>    fs/f2fs/Kconfig             |   9 +++
>>
>> I try to apply this patch in my local dev branch, but it failed due to
>> conflicting with below commit, it needs to rebase this patch to last dev
>> branch.
> 
> I applied this in dev branch. Could you please check?

Yeah, I see.

>>> +config F2FS_IOSTAT_IO_LATENCY
>>> +	bool "F2FS IO statistics IO latency information"
>>> +	depends on F2FS_FS
>>> +	default n
>>> +	help
>>> +	  Support printing out periodic IO latency statistics tracepoint
>>> +	  events. With this, you have to turn on "iostat_enable" sysfs
>>> +	  node to print this out.
>>
>> This functionality looks independent, how about introuducing iostat.h
>> and iostat.c (not sure, maybe trace.[hc])to include newly added structure
>> and functions for dispersive codes cleanup.

Thoughts? this also can avoid using CONFIG_F2FS_IOSTAT_IO_LATENCY in many places.

Thanks,