linux-kernel - Re: [PATCH net-next v3 01/11] net/smc: adapt SMC-D device dump for Emulated-ISM

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Date: Fri, 15 Mar 2024 11:44:16 +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 2024/3/14 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.

> # 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?

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 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.

> 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.

> 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!

> 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))