netdev - Re: [PATCH bpf-next v2 1/2] net/smc: Introduce BPF injection capability for SMC

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Date:   Fri, 24 Mar 2023 12:08:59 +0800
From:   "D. Wythe" <alibuda@...ux.alibaba.com>
To:     Martin KaFai Lau <martin.lau@...ux.dev>
Cc:     kuba@...nel.org, davem@...emloft.net, netdev@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-rdma@...r.kernel.org,
        bpf@...r.kernel.org, kgraul@...ux.ibm.com, wenjia@...ux.ibm.com,
        jaka@...ux.ibm.com, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org
Subject: Re: [PATCH bpf-next v2 1/2] net/smc: Introduce BPF injection
 capability for SMC



On 3/24/23 4:46 AM, Martin KaFai Lau wrote:
> On 3/9/23 3:49 AM, D. Wythe wrote:
>>>> --- /dev/null
>>>> +++ b/net/smc/bpf_smc_struct_ops.c
>>>> @@ -0,0 +1,146 @@
>>>> +// SPDX-License-Identifier: GPL-2.0
>>>> +
>>>> +#include <linux/kernel.h>
>>>> +#include <linux/bpf_verifier.h>
>>>> +#include <linux/btf_ids.h>
>>>> +#include <linux/bpf.h>
>>>> +#include <linux/btf.h>
>>>> +#include <net/sock.h>
>>>> +#include <net/smc.h>
>>>> +
>>>> +extern struct bpf_struct_ops smc_sock_negotiator_ops;
>>>> +
>>>> +DEFINE_RWLOCK(smc_sock_negotiator_ops_rwlock);
>>>> +struct smc_sock_negotiator_ops *negotiator;
>>>
>>> Is it sure one global negotiator (policy) will work for all 
>>> smc_sock? or each sk should have its own negotiator and the 
>>> negotiator is selected by setsockopt.
>>>
>> This is really a good question,  we can really consider adding an 
>> independent negotiator for each sock.
>>
>> But just like the TCP congestion control , the global negotiator can 
>> be used for sock without
>>
>> special requirements.
>
> It is different from TCP congestion control (CC). TCP CC has a global 
> default but each sk can select what tcp-cc to use and there can be 
> multiple tcp-cc registered under different names.
>
> It sounds like smc using tcp_sock should be able to have different 
> negotiator also (eg. based on dst IP or some other tcp connection 
> characteristic). The tcp-cc registration, per-sock selection and the 
> rcu_read_lock+refcnt are well understood and there are other bpf 
> infrastructure to support the per sock tcp-cc selection (like 
> bpf_setsockopt).
>
> For the network stack, there is little reason other af_* should not 
> follow at the beginning considering the infrastructure has already 
> been built. The one single global negotiator and reader/writer lock in 
> this patch reads like an effort wanted to give it a try and see if it 
> will be useful before implementing the whole thing. It is better to 
> keep it off the tree for now until it is more ready.

Hi Martin,

Thank you very much for your comments. I have indeed removed global 
negotiator from my latest implementation.

The latest design is that users can register a negotiator implementation 
indexed by name, smc_sock can use bpf_setsockopt to specify
whether a specific negotiation implementation is required via name. If 
there are no settings, there will be no negotiators.

What do you think?

In addition, I am very sorry that I have not issued my implementation 
for such a long time, and I have encountered some problems with the 
implementation because
the SMC needs to be built as kernel module, I have struggled with the 
bpf_setsockopt implementation, and there are some new self-testes that 
need to be written.

However, I believe that I can send a new version as soon as possible.


Best wishes
D. Wythe