Date: Fri, 15 Mar 2024 20:29:26 +0800
From: Wen Gu <guwen@...ux.alibaba.com>
To: Jan Karcher <jaka@...ux.ibm.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 2024/3/15 18:27, Jan Karcher wrote:
> 
> 
> 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?
> 

Understand, a long-term view is better.

>>
>>> # 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.
> 

Make sense to me.

>>
>>> 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, ...) |
> +--------------------+
> 
> 

I like this diagram and it is very clear. So core information will be applicable to all ISM devices,
and the extension information will be specific to some certain kinds.

>>
>>> 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.
>

Sure! and thank you very much!


Best regards,
Wen Gu

>> >>> 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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