linux-kernel - Re: [PATCH net-next 09/15] net/smc: introduce loopback-ism statistics attributes

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Message-ID: <700198c8-e4dc-4974-9ebf-f819deaa785b@linux.ibm.com>
Date: Fri, 23 Feb 2024 15:13:18 +0100
From: Wenjia Zhang <wenjia@...ux.ibm.com>
To: Wen Gu <guwen@...ux.alibaba.com>, wintera@...ux.ibm.com, hca@...ux.ibm.com,
        gor@...ux.ibm.com, agordeev@...ux.ibm.com, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        jaka@...ux.ibm.com
Cc: borntraeger@...ux.ibm.com, svens@...ux.ibm.com, alibuda@...ux.alibaba.com,
        tonylu@...ux.alibaba.com, linux-s390@...r.kernel.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 09/15] net/smc: introduce loopback-ism statistics
 attributes



On 20.02.24 03:45, Wen Gu wrote:
> 
> 
> On 2024/2/16 22:24, Wenjia Zhang wrote:
>>
>>
>> On 11.01.24 13:00, Wen Gu wrote:
>>> This introduces some statistics attributes of loopback-ism. They can be
>>> read from /sys/devices/virtual/smc/loopback-ism/{xfer_tytes|dmbs_cnt}.
>>>
>>> Signed-off-by: Wen Gu <guwen@...ux.alibaba.com>
>>> ---
>>>   net/smc/smc_loopback.c | 74 ++++++++++++++++++++++++++++++++++++++++++
>>>   net/smc/smc_loopback.h | 22 +++++++++++++
>>>   2 files changed, 96 insertions(+)
>>>
>>
>> I've read the comments from Jiri and your answer. I can understand 
>> your thought. However, from the perspective of the end user, it makes 
>> more sense to integetrate the stats info into 'smcd stats'. Otherwise, 
>> it would make users confused to find out with which tool to check 
>> which statisic infornation. Sure, some improvement of the smc-tools is 
>> also needed
> 
> Thank you Wenjia.
> 
> Let's draw an analogy with RDMA devices, which is used in SMC-R. If we want
> to check the RNIC status or statistics, we may use rdma statistic 
> command, or
> ibv_devinfo command, or check file under /sys/class/infiniband/mlx5_0. 
> These
> provide details or attributes related to *devices*.
> 
> Since s390 ISM can be used out of SMC, I guess it also has its own way 
> (other
> than smc-tools) to check the statistic?
> 
> What we can see in smcr stats or smcd stats command is about statistic or
> status of SMC *protocol* layer, such as DMB status, Tx/Rx, connections, 
> fallbacks.
> 
> If we put the underlying devices's statistics into smc-tools, should we 
> also
> put RNIC statistics or s390 ISM statistics into smcr stat or smcd stat? and
> for each futures device that can be used by SMC-R/SMC-D, should we 
> update them
> into smcr stat and smcd stat? And the attributes of each devices may be 
> different,
> should we add entries in smcd stat for each of them?
> 
> After considering the above things, I believe that the details of the 
> underlying
> device should not be exposed to smc(smc-tools). What do you think?
> 
> Thanks!
> 
That is a very good point. It really depends on how we understand 
*devices* and how we want to use it. The more we are thinking, the more 
complicated the thing is getting. I'm trying to find accurate 
definitions on modeling virtual devices hoping that would make things 
eaiser. Unfortunately, it is not easy. Finally, I found this article: 
https://lwn.net/Articles/645810/ (Heads up! It is even from nine years 
ago, I'm not sure how reliable it is.) With the insight of this article, 
I'm trying to summarize my thought:

It looks good to put the loopback-ism under the /sys/devices/virtual, 
especially according to the article
"
.. it is simply a place to put things that don't belong anywhere else.
"
However, in practice we use this in the term of simulated ism, which 
includes not only loopback-ism, but also other ones. Thus, does it not 
make sense to classify all of them together? E.g. same bus (just a 
half-baked idea)

Then the following questions are comig up:
- How should we organize them?
- Should it show up in the smc_rnics?
- How should it be seen from the perspective of the container?
- If we see this loopback-ism as a *device*, should we not only put the 
device related information under the /sys? Thus, dmbs_cnt seems ok, but 
xfer_tytes not. Besides, we have a field in smd stat naming "Data 
transmitted (Bytes)", which should be suitable for this information.