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([2620:10d:c090:400::5:87c3]) by smtp.gmail.com with ESMTPSA id v3-20020a170902b7c300b0019fcece6847sm2022912plz.227.2023.03.17.16.07.24 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 17 Mar 2023 16:07:25 -0700 (PDT) Message-ID: <4271f277-ec08-ea15-4c7b-8c5147db6308@gmail.com> Date: Fri, 17 Mar 2023 16:07:22 -0700 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 Subject: Re: [PATCH bpf-next v7 2/8] net: Update an existing TCP congestion control algorithm. Content-Language: en-US, en-ZW To: Daniel Borkmann , Kui-Feng Lee , bpf@vger.kernel.org, ast@kernel.org, martin.lau@linux.dev, song@kernel.org, kernel-team@meta.com, andrii@kernel.org, sdf@google.com Cc: netdev@vger.kernel.org, Eric Dumazet References: <20230316023641.2092778-1-kuifeng@meta.com> <20230316023641.2092778-3-kuifeng@meta.com> From: Kui-Feng Lee In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 3/17/23 08:23, Daniel Borkmann wrote: > On 3/16/23 3:36 AM, 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 purpose is to update a customized algorithm implemented in BPF >> struct_ops with a new version on the flight.  The following is an >> example of using the userspace API implemented in later BPF patches. >> >>     link = bpf_map__attach_struct_ops(skel->maps.ca_update_1); >>     ....... >>     err = bpf_link__update_map(link, skel->maps.ca_update_2); >> >> We first load and register an algorithm implemented in BPF struct_ops, >> then swap it out with a new one using the same name. After that, newly >> created connections will apply the updated algorithm, while older ones >> retain the previous version already applied. >> >> This patch also takes this chance to refactor the ca validation into >> the new tcp_validate_congestion_control() function. >> >> Cc: netdev@vger.kernel.org, Eric Dumazet >> Signed-off-by: Kui-Feng Lee >> --- >>   include/net/tcp.h   |  3 +++ >>   net/ipv4/tcp_cong.c | 60 +++++++++++++++++++++++++++++++++++++++------ >>   2 files changed, 56 insertions(+), 7 deletions(-) >> >> diff --git a/include/net/tcp.h b/include/net/tcp.h >> index db9f828e9d1e..2abb755e6a3a 100644 >> --- a/include/net/tcp.h >> +++ b/include/net/tcp.h >> @@ -1117,6 +1117,9 @@ 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); >> +int tcp_validate_congestion_control(struct tcp_congestion_ops *ca); >>   void tcp_assign_congestion_control(struct sock *sk); >>   void tcp_init_congestion_control(struct sock *sk); >> diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c >> index db8b4b488c31..c90791ae8389 100644 >> --- a/net/ipv4/tcp_cong.c >> +++ b/net/ipv4/tcp_cong.c >> @@ -75,14 +75,8 @@ struct tcp_congestion_ops *tcp_ca_find_key(u32 key) >>       return NULL; >>   } >> -/* >> - * Attach new congestion control algorithm to the list >> - * of available options. >> - */ >> -int tcp_register_congestion_control(struct tcp_congestion_ops *ca) >> +int tcp_validate_congestion_control(struct tcp_congestion_ops *ca) >>   { >> -    int ret = 0; >> - >>       /* all algorithms must implement these */ >>       if (!ca->ssthresh || !ca->undo_cwnd || >>           !(ca->cong_avoid || ca->cong_control)) { >> @@ -90,6 +84,20 @@ int tcp_register_congestion_control(struct >> tcp_congestion_ops *ca) >>           return -EINVAL; >>       } >> +    return 0; >> +} >> + >> +/* Attach new congestion control algorithm to the list >> + * of available options. >> + */ >> +int tcp_register_congestion_control(struct tcp_congestion_ops *ca) >> +{ >> +    int ret; >> + >> +    ret = tcp_validate_congestion_control(ca); >> +    if (ret) >> +        return ret; >> + >>       ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name)); >>       spin_lock(&tcp_cong_list_lock); >> @@ -130,6 +138,44 @@ void tcp_unregister_congestion_control(struct >> tcp_congestion_ops *ca) >>   } >>   EXPORT_SYMBOL_GPL(tcp_unregister_congestion_control); >> +/* Replace a registered old ca with a new one. >> + * >> + * The new ca must have the same name as the old one, that has been >> + * registered. >> + */ >> +int tcp_update_congestion_control(struct tcp_congestion_ops *ca, >> struct tcp_congestion_ops *old_ca) >> +{ >> +    struct tcp_congestion_ops *existing; >> +    int ret; >> + >> +    ret = tcp_validate_congestion_control(ca); >> +    if (ret) >> +        return ret; >> + >> +    ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name)); >> + >> +    spin_lock(&tcp_cong_list_lock); >> +    existing = tcp_ca_find_key(old_ca->key); >> +    if (ca->key == TCP_CA_UNSPEC || !existing || >> strcmp(existing->name, ca->name)) { >> +        pr_notice("%s not registered or non-unique key\n", >> +              ca->name); >> +        ret = -EINVAL; >> +    } else if (existing != old_ca) { >> +        pr_notice("invalid old congestion control algorithm to >> replace\n"); >> +        ret = -EINVAL; >> +    } else { >> +        /* Add the new one before removing the old one to keep >> +         * one implementation available all the time. >> +         */ >> +        list_add_tail_rcu(&ca->list, &tcp_cong_list); >> +        list_del_rcu(&existing->list); >> +        pr_debug("%s updated\n", ca->name); >> +    } >> +    spin_unlock(&tcp_cong_list_lock); >> + >> +    return ret; >> +} > > Was wondering if we could have tcp_register_congestion_control and > tcp_update_congestion_control > could be refactored for reuse. Maybe like below. From the function > itself what is not clear whether > callers that replace an existing one should do the synchronize_rcu() > themselves or if this should > be part of tcp_update_congestion_control? > > int tcp_check_congestion_control(struct tcp_congestion_ops *ca) > { >     /* All algorithms must implement these. */ >     if (!ca->ssthresh || !ca->undo_cwnd || >         !(ca->cong_avoid || ca->cong_control)) { >         pr_err("%s does not implement required ops\n", ca->name); >         return -EINVAL; >     } >     if (ca->key == TCP_CA_UNSPEC) >         ca->key = jhash(ca->name, sizeof(ca->name), strlen(ca->name)); >     if (ca->key == TCP_CA_UNSPEC) { >         pr_notice("%s results in zero key\n", ca->name); >         return -EEXIST; >     } >     return 0; > } > > /* Attach new congestion control algorithm to the list of available >  * options or replace an existing one if old is non-NULL. >  */ > int tcp_update_congestion_control(struct tcp_congestion_ops *new, >                   struct tcp_congestion_ops *old) > { >     struct tcp_congestion_ops *found; >     int ret; > >     ret = tcp_check_congestion_control(new); >     if (ret) >         return ret; >     if (old && >         (old->key != new->key || >          strcmp(old->name, new->name))) { >         pr_notice("%s & %s have non-matching congestion control names\n", >               old->name, new->name); >         return -EINVAL; >     } >     spin_lock(&tcp_cong_list_lock); >     found = tcp_ca_find_key(new->key); >     if (old) { >         if (found == old) { >             list_add_tail_rcu(&new->list, &tcp_cong_list); >             list_del_rcu(&old->list); >         } else { >             pr_notice("%s not registered\n", old->name); >             ret = -EINVAL; >         } >     } else { >         if (found) { >             pr_notice("%s already registered\n", new->name); >             ret = -EEXIST; >         } else { >             list_add_tail_rcu(&new->list, &tcp_cong_list); >         } >     } >     spin_unlock(&tcp_cong_list_lock); >     return ret; > } After trying to do this refactoring, I found it just shares a few lines of code, but make thing complicated by adding more checks. So, I prefer to keep it as it is. How do you think? > > int tcp_register_congestion_control(struct tcp_congestion_ops *ca) > { >     return tcp_update_congestion_control(ca, NULL); > } > EXPORT_SYMBOL_GPL(tcp_register_congestion_control);