netdev - Re: [PATCH bpf-next v6 2/8] net: Update an existing TCP congestion control algorithm.

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Date:   Mon, 13 Mar 2023 21:31:20 -0700
From:   Kui-Feng Lee <sinquersw@...il.com>
To:     Martin KaFai Lau <martin.lau@...ux.dev>,
        Kui-Feng Lee <kuifeng@...a.com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org, ast@...nel.org,
        song@...nel.org, kernel-team@...a.com, andrii@...nel.org,
        sdf@...gle.com
Subject: Re: [PATCH bpf-next v6 2/8] net: Update an existing TCP congestion
 control algorithm.



On 3/13/23 17:28, Martin KaFai Lau wrote:
> On 3/9/23 8:38 PM, Kui-Feng Lee wrote:
>> This feature lets you immediately transition to another congestion
>> control algorithm or implementation with the same name.  Once a name
>> is updated, new connections will apply this new algorithm.
> 
> The commit message needs to explain why the change is needed and some 
> major details on how the patch is doing it. In this case, why a later 
> bpf patch needs it and what major changes are made to tcp_cong.c.
> 
> For example,
> 
> A later bpf patch will allow attaching a bpf_struct_ops (TCP Congestion 
> Control implemented in bpf) to bpf_link. The later bpf patch will also 
> use the existing bpf_link API to replace a bpf_struct_ops (ie. to 
> replace an old tcp-cc with a new tcp-cc under the same name). This 
> requires a helper function to replace a tcp-cc under a 
> tcp_cong_list_lock. Thus, this patch adds a 
> tcp_update_congestion_control() to replace the "old_ca" with a new "ca".
> 
> This patch also takes this chance to refactor the ca validation into the 
> new tcp_validate_congestion_control() function.


Sure!

> 
>>
>> Signed-off-by: Kui-Feng Lee <kuifeng@...a.com>
>> ---
>>   include/linux/bpf.h            |  1 +
>>   include/net/tcp.h              |  2 ++
>>   net/bpf/bpf_dummy_struct_ops.c |  6 ++++
>>   net/ipv4/bpf_tcp_ca.c          |  6 ++++
>>   net/ipv4/tcp_cong.c            | 60 ++++++++++++++++++++++++++++++----
>>   5 files changed, 68 insertions(+), 7 deletions(-)
>>
>> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
>> index 00ca92ea6f2e..0f84925d66db 100644
>> --- a/include/linux/bpf.h
>> +++ b/include/linux/bpf.h
>> @@ -1511,6 +1511,7 @@ struct bpf_struct_ops {
>>                  void *kdata, const void *udata);
>>       int (*reg)(void *kdata);
>>       void (*unreg)(void *kdata);
>> +    int (*update)(void *kdata, void *old_kdata);
>>       const struct btf_type *type;
>>       const struct btf_type *value_type;
>>       const char *name;
>> diff --git a/include/net/tcp.h b/include/net/tcp.h
>> index db9f828e9d1e..239cc0e2639c 100644
>> --- a/include/net/tcp.h
>> +++ b/include/net/tcp.h
>> @@ -1117,6 +1117,8 @@ struct tcp_congestion_ops {
>>   int tcp_register_congestion_control(struct tcp_congestion_ops *type);
>>   void tcp_unregister_congestion_control(struct tcp_congestion_ops 
>> *type);
>> +int tcp_update_congestion_control(struct tcp_congestion_ops *type,
>> +                  struct tcp_congestion_ops *old_type);
>>   void tcp_assign_congestion_control(struct sock *sk);
>>   void tcp_init_congestion_control(struct sock *sk);
>> diff --git a/net/bpf/bpf_dummy_struct_ops.c 
>> b/net/bpf/bpf_dummy_struct_ops.c
>> index ff4f89a2b02a..158f14e240d0 100644
>> --- a/net/bpf/bpf_dummy_struct_ops.c
>> +++ b/net/bpf/bpf_dummy_struct_ops.c
>> @@ -222,12 +222,18 @@ static void bpf_dummy_unreg(void *kdata)
>>   {
>>   }
>> +static int bpf_dummy_update(void *kdata, void *old_kdata)
>> +{
>> +    return -EOPNOTSUPP;
>> +}
>> +
>>   struct bpf_struct_ops bpf_bpf_dummy_ops = {
>>       .verifier_ops = &bpf_dummy_verifier_ops,
>>       .init = bpf_dummy_init,
>>       .check_member = bpf_dummy_ops_check_member,
>>       .init_member = bpf_dummy_init_member,
>>       .reg = bpf_dummy_reg,
>> +    .update = bpf_dummy_update,
>>       .unreg = bpf_dummy_unreg,
>>       .name = "bpf_dummy_ops",
>>   };
>> diff --git a/net/ipv4/bpf_tcp_ca.c b/net/ipv4/bpf_tcp_ca.c
>> index 13fc0c185cd9..66ce5fadfe42 100644
>> --- a/net/ipv4/bpf_tcp_ca.c
>> +++ b/net/ipv4/bpf_tcp_ca.c
>> @@ -266,10 +266,16 @@ static void bpf_tcp_ca_unreg(void *kdata)
>>       tcp_unregister_congestion_control(kdata);
>>   }
>> +static int bpf_tcp_ca_update(void *kdata, void *old_kdata)
>> +{
>> +    return tcp_update_congestion_control(kdata, old_kdata);
>> +}
>> +
>>   struct bpf_struct_ops bpf_tcp_congestion_ops = {
>>       .verifier_ops = &bpf_tcp_ca_verifier_ops,
>>       .reg = bpf_tcp_ca_reg,
>>       .unreg = bpf_tcp_ca_unreg,
>> +    .update = bpf_tcp_ca_update,
> 
> In v5, a comment was given to move the ".update" related changes to 
> patch 5 such that patch 2 will only have netdev change in tcp_cong.c for 
> review purpose.
> 
> Please ensure the earlier review comment is addressed in the next 
> revision or reply if the earlier review comment does not make sense. 
> This will save time for the reviewer not to have to repeat the same 
> comment again.

Sorry about this.  I only addressed .validate and missed .update.
Will fix this.

> 
>>       .check_member = bpf_tcp_ca_check_member,
>>       .init_member = bpf_tcp_ca_init_member,
>>       .init = bpf_tcp_ca_init,
> 
>