Date: Fri, 15 Mar 2024 11:27:27 +0100
From: Jan Karcher <jaka@...ux.ibm.com>
To: Wen Gu <guwen@...ux.alibaba.com>, wintera@...ux.ibm.com,
        twinkler@...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, wenjia@...ux.ibm.com
Cc: borntraeger@...ux.ibm.com, svens@...ux.ibm.com, alibuda@...ux.alibaba.com,
        tonylu@...ux.alibaba.com, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v3 01/11] net/smc: adapt SMC-D device dump for
 Emulated-ISM



On 15/03/2024 04:44, Wen Gu wrote:
> 
> 
> On 2024/3/14 18:23, Jan Karcher wrote:
>>
>>
>> On 12/03/2024 15:27, Wen Gu wrote:
>>> The introduction of Emulated-ISM requires adaptation of SMC-D device
>>> dump. Software implemented non-PCI device (loopback-ism) should be
>>> handled correctly and the CHID reserved for Emulated-ISM should be got
>>> from smcd_ops interface instead of PCI information.
>>>
>>> Signed-off-by: Wen Gu <guwen@...ux.alibaba.com>
>>> ---
>>>   net/smc/smc_ism.c | 13 ++++++++++---
>>>   1 file changed, 10 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/net/smc/smc_ism.c b/net/smc/smc_ism.c
>>> index ac88de2a06a0..b6eca4231913 100644
>>> --- a/net/smc/smc_ism.c
>>> +++ b/net/smc/smc_ism.c
>>> @@ -252,12 +252,11 @@ static int smc_nl_handle_smcd_dev(struct 
>>> smcd_dev *smcd,
>>>       char smc_pnet[SMC_MAX_PNETID_LEN + 1];
>>>       struct smc_pci_dev smc_pci_dev;
>>>       struct nlattr *port_attrs;
>>> +    struct device *device;
>>>       struct nlattr *attrs;
>>> -    struct ism_dev *ism;
>>>       int use_cnt = 0;
>>>       void *nlh;
>>> -    ism = smcd->priv;
>>>       nlh = genlmsg_put(skb, NETLINK_CB(cb->skb).portid, 
>>> cb->nlh->nlmsg_seq,
>>>                 &smc_gen_nl_family, NLM_F_MULTI,
>>>                 SMC_NETLINK_GET_DEV_SMCD);
>>> @@ -272,7 +271,15 @@ static int smc_nl_handle_smcd_dev(struct 
>>> smcd_dev *smcd,
>>>       if (nla_put_u8(skb, SMC_NLA_DEV_IS_CRIT, use_cnt > 0))
>>>           goto errattr;
>>>       memset(&smc_pci_dev, 0, sizeof(smc_pci_dev));
>>> -    smc_set_pci_values(to_pci_dev(ism->dev.parent), &smc_pci_dev);
>>> +    device = smcd->ops->get_dev(smcd);
>>> +    if (device->parent)
>>> +        smc_set_pci_values(to_pci_dev(device->parent), &smc_pci_dev);
>>> +    if (smc_ism_is_emulated(smcd)) {
>>> +        smc_pci_dev.pci_pchid = smc_ism_get_chid(smcd);
>>> +        if (!device->parent)
>>> +            snprintf(smc_pci_dev.pci_id, sizeof(smc_pci_dev.pci_id),
>>> +                 "%s", dev_name(device));
>>> +    }
>>
>> Hi Wen Gu,
>>
>> playing around with the loopback-ism device and testing it, i 
>> developed some concerns regarding this exposure. Basically this 
>> enables us to see the loopback device in the `smcd device` tool 
>> without any changes.
>> E.g.:
>> ```
>> # smcd device
>> FID  Type  PCI-ID        PCHID  InUse  #LGs  PNET-ID
>> 0000 0     loopback-ism  ffff   No        0
>> 102a ISM   0000:00:00.0  07c2   No        0  NET1
>> ```
>>
>> Now the problem with this is that "loopback-ism" is no valid PCI-ID 
>> and should not be there. My first thought was to put an "n/a" instead, 
>> but that opens up another problem. Currently you could set - even if 
>> it does not make sense - a PNET_ID for the loopback device:
>> ```
> 
> Yes, and we can exclude loopback-ism in smc_pnet_enter() if necessary.

We could, but we have to make sure we implement those distinctions at 
the right location. E.g.: if virtio-ism is coming. Does a PNETID make 
sense for a virtio-ism device? Do we want to exclude is also there or do 
we want an abstracted layer/mechanism to recognize if a device has a 
PNETId capability or not?

> 
>> # smc_pnet -a -D loopback-ism NET1
>> # smcd device
>> FID  Type  PCI-ID        PCHID  InUse  #LGs  PNET-ID
>> 0000 0     loopback-ism  ffff   No        0  *NET1
>> 102a ISM   0000:00:00.0  07c2   No        0  NET1
>> ```
>> If we would change the PCI-ID to "n/a" it would be a valid input 
>> parameter for the tooling which is... to put it nice... not so beautiful.
> 
> FID  Type  PCI-ID        PCHID  InUse  #LGs  PNET-ID
> 0000 0     n/a           ffff   No        0
> 
> IIUC, the problem is that the 'n/a', which would be an input for other 
> tools, is somewhat strange?

Exactly.

> 
> Since PCHID 0xffff is clear defined for loopback-ism, I am wondering if 
> it can be a specific sign
> of loopback-ism for tooling to not take PCI-ID into account? Would you 
> also consider that inelegant?

I think deciding on PCHID is the only way we can currently differentiate 
what kind of device we are talking about. So my guess would be that 
PCHID is going to play a big role in future design decisions.

> 
>> I brainstormed this with them team and the problem is more complex.
>> In theory there shouldn't be PCI information set for the loopback 
>> device. There should be a better abstraction in the netlink interface 
>> that creates this output and the tooling should be made aware of it.
>>
> 
> Yes, it is better. But I couldn't surely picture how the abstraction 
> looks like, and if it is necessary
> to introduce it just for a special case of loopback-ism (note that 
> virtio-ISM also has PCI information),
> since we can identify loopback-ism by CHID.

Please take the following with a grain of salt. I just want to give you 
a bit insight of our current train of thought. None of it is final or 
set in stone. The idea would be to have device core information that 
contain the information which other fields are important for this 
device. And corresponding "extensions" that contain the information. The 
tooling cvould then decide soley on the core information which features 
are supported by a device and which are not.
If that is really needed: Not sure yet. Is this the best solution: 
Propably not.
E.g.:

SMC-D netlink abstraction

+------------------------------------+
| Core information                   |
| (e.g. PCHID, InUse, isPCI, isS390) |
+------------------------------------+

+----------------+
| s390 extension |
| (e.g.FID)      |
+----------------+

+--------------------+
| PCI extension      |
| (e.g. PCI-ID, ...) |
+--------------------+


> 
>> Do you rely on the output currently? What are your thoughts about it?
>> If not I'd ask you to not fill the netlink interface for the loopback 
>> device and refactor it with the next stage when we create a right 
>> interface for it.
>>
> 
> Currently we don't rely on the output, and I have no objection to the 
> proposal that not fill the netlink
> interface for loopback-ism and refactor it in the next stage.

Thank you! If you have ideas regarding the design of the interface hit 
us up. As soon as we are going to think about this further I'm going to 
invite you to those discussions.

> 
>> Since the Merge-Window is closed feel free to send new versions as RFC.
> 
> OK, I will send the new version as an RFC.
> 
> Thank you!

Thanks!
- Jan

> 
>> Thank you
>> - Jan
>>
>>>       if (nla_put_u32(skb, SMC_NLA_DEV_PCI_FID, smc_pci_dev.pci_fid))
>>>           goto errattr;
>>>       if (nla_put_u16(skb, SMC_NLA_DEV_PCI_CHID, smc_pci_dev.pci_pchid))

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