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Subject: Re: [RFC PATCH] ceph: add remote object copy counter to fs client
To:     Patrick Donnelly <pdonnell@redhat.com>,
        Jeff Layton <jlayton@kernel.org>
Cc:     =?UTF-8?Q?Lu=c3=ads_Henriques?= <lhenriques@suse.de>,
        Ilya Dryomov <idryomov@gmail.com>,
        Ceph Development <ceph-devel@vger.kernel.org>,
        linux-kernel@vger.kernel.org
References: <20211020143708.14728-1-lhenriques@suse.de>
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From:   Xiubo Li <xiubli@redhat.com>
Message-ID: <785d1435-4a2c-95aa-0573-2de54b4e7b6b@redhat.com>
Date:   Tue, 26 Oct 2021 11:05:58 +0800
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On 10/22/21 1:30 AM, Patrick Donnelly wrote:
> On Thu, Oct 21, 2021 at 12:35 PM Jeff Layton <jlayton@kernel.org> wrote:
>> On Thu, 2021-10-21 at 12:18 -0400, Patrick Donnelly wrote:
>>> On Thu, Oct 21, 2021 at 11:44 AM Jeff Layton <jlayton@kernel.org> wrote:
>>>> On Thu, 2021-10-21 at 09:52 -0400, Patrick Donnelly wrote:
>>>>> On Wed, Oct 20, 2021 at 12:27 PM Jeff Layton <jlayton@kernel.org> wrote:
>>>>>> On Wed, 2021-10-20 at 15:37 +0100, Luís Henriques wrote:
>>>>>>> This counter will keep track of the number of remote object copies done on
>>>>>>> copy_file_range syscalls.  This counter will be filesystem per-client, and
>>>>>>> can be accessed from the client debugfs directory.
>>>>>>>
>>>>>>> Cc: Patrick Donnelly <pdonnell@redhat.com>
>>>>>>> Signed-off-by: Luís Henriques <lhenriques@suse.de>
>>>>>>> ---
>>>>>>> This is an RFC to reply to Patrick's request in [0].  Note that I'm not
>>>>>>> 100% sure about the usefulness of this patch, or if this is the best way
>>>>>>> to provide the functionality Patrick requested.  Anyway, this is just to
>>>>>>> get some feedback, hence the RFC.
>>>>>>>
>>>>>>> Cheers,
>>>>>>> --
>>>>>>> Luís
>>>>>>>
>>>>>>> [0] https://github.com/ceph/ceph/pull/42720
>>>>>>>
>>>>>> I think this would be better integrated into the stats infrastructure.
>>>>>>
>>>>>> Maybe you could add a new set of "copy" stats to struct
>>>>>> ceph_client_metric that tracks the total copy operations done, their
>>>>>> size and latency (similar to read and write ops)?
>>>>> I think it's a good idea to integrate this into "stats" but I think a
>>>>> local debugfs file for some counters is still useful. The "stats"
>>>>> module is immature at this time and I'd rather not build any qa tests
>>>>> (yet) that rely on it.
>>>>>
>>>>> Can we generalize this patch-set to a file named "op_counters" or
>>>>> similar and additionally add other OSD ops performed by the kclient?
>>>>>
>>>>
>>>> Tracking this sort of thing is the main purpose of the stats code. I'm
>>>> really not keen on adding a whole separate set of files for reporting
>>>> this.
>>> Maybe I'm confused. Is there some "file" which is already used for
>>> this type of debugging information? Or do you mean the code for
>>> sending stats to the MDS to support cephfs-top?
>>>
>>>> What's the specific problem with relying on the data in debugfs
>>>> "metrics" file?
>>> Maybe no problem? I wasn't aware of a "metrics" file.
>>>
>> Yes. For instance:
>>
>> # cat /sys/kernel/debug/ceph/*/metrics
>> item                               total
>> ------------------------------------------
>> opened files  / total inodes       0 / 4
>> pinned i_caps / total inodes       5 / 4
>> opened inodes / total inodes       0 / 4
>>
>> item          total       avg_lat(us)     min_lat(us)     max_lat(us)     stdev(us)
>> -----------------------------------------------------------------------------------
>> read          0           0               0               0               0
>> write         5           914013          824797          1092343         103476
>> metadata      79          12856           1572            114572          13262
>>
>> item          total       avg_sz(bytes)   min_sz(bytes)   max_sz(bytes)  total_sz(bytes)
>> ----------------------------------------------------------------------------------------
>> read          0           0               0               0               0
>> write         5           4194304         4194304         4194304         20971520
>>
>> item          total           miss            hit
>> -------------------------------------------------
>> d_lease       11              0               29
>> caps          5               68              10702
>>
>>
>> I'm proposing that Luis add new lines for "copy" to go along with the
>> "read" and "write" ones. The "total" counter should give you a count of
>> the number of operations.
> Okay that makes more sense!
>
> Side note: I am a bit horrified by how computer-unfriendly that
> table-formatted data is.

Any suggestion to improve this ?

How about just make the "metric" file writable like a switch ? And as 
default it will show the data as above and if tools want the 
computer-friendly format, just write none-zero to it, then show raw data 
just like:

# cat /sys/kernel/debug/ceph/*/metrics
opened_files:0
pinned_i_caps:5
opened_inodes:0
total_inodes:4

read_latency:0,0,0,0,0
write_latency:5,914013,824797,1092343,103476
metadata_latency:79,12856,1572,114572,13262

read_size:0,0,0,0,0
write_size:5,4194304,4194304,4194304,20971520

d_lease:11,0,29
caps:5,68,10702