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From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Thu, 12 Dec 2019 21:16:04 -0800
Message-ID: <CAADnVQLh9Dz82YUMCR7P0sHed9W+bkcGXw098E3dwO5rHTmZ2g@mail.gmail.com>
Subject: Re: [PATCH v3 bpf-next 00/11] add bpf batch ops to process more than
 1 elem
To:     Brian Vazquez <brianvv@google.com>
Cc:     Brian Vazquez <brianvv.kernel@gmail.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        "David S . Miller" <davem@davemloft.net>,
        Yonghong Song <yhs@fb.com>,
        Stanislav Fomichev <sdf@google.com>,
        Petar Penkov <ppenkov@google.com>,
        Willem de Bruijn <willemb@google.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Network Development <netdev@vger.kernel.org>,
        bpf <bpf@vger.kernel.org>
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On Wed, Dec 11, 2019 at 2:34 PM Brian Vazquez <brianvv@google.com> wrote:
>
> This patch series introduce batch ops that can be added to bpf maps to
> lookup/lookup_and_delete/update/delete more than 1 element at the time,
> this is specially useful when syscall overhead is a problem and in case
> of hmap it will provide a reliable way of traversing them.
>
> The implementation inclues a generic approach that could potentially be
> used by any bpf map and adds it to arraymap, it also includes the specific
> implementation of hashmaps which are traversed using buckets instead
> of keys.
>
> The bpf syscall subcommands introduced are:
>
>   BPF_MAP_LOOKUP_BATCH
>   BPF_MAP_LOOKUP_AND_DELETE_BATCH
>   BPF_MAP_UPDATE_BATCH
>   BPF_MAP_DELETE_BATCH
>
> The UAPI attribute is:
>
>   struct { /* struct used by BPF_MAP_*_BATCH commands */
>          __aligned_u64   in_batch;       /* start batch,
>                                           * NULL to start from beginning
>                                           */
>          __aligned_u64   out_batch;      /* output: next start batch */
>          __aligned_u64   keys;
>          __aligned_u64   values;
>          __u32           count;          /* input/output:
>                                           * input: # of key/value
>                                           * elements
>                                           * output: # of filled elements
>                                           */
>          __u32           map_fd;
>          __u64           elem_flags;
>          __u64           flags;
>   } batch;
>
>
> in_batch and out_batch are only used for lookup and lookup_and_delete since
> those are the only two operations that attempt to traverse the map.
>
> update/delete batch ops should provide the keys/values that user wants
> to modify.
>
> Here are the previous discussions on the batch processing:
>  - https://lore.kernel.org/bpf/20190724165803.87470-1-brianvv@google.com/
>  - https://lore.kernel.org/bpf/20190829064502.2750303-1-yhs@fb.com/
>  - https://lore.kernel.org/bpf/20190906225434.3635421-1-yhs@fb.com/
>
> Changelog sinve v2:
>  - Add generic batch support for lpm_trie and test it (Yonghong Song)
>  - Use define MAP_LOOKUP_RETRIES for retries (John Fastabend)
>  - Return errors directly and remove labels (Yonghong Song)
>  - Insert new API functions into libbpf alphabetically (Yonghong Song)
>  - Change hlist_nulls_for_each_entry_rcu to
>    hlist_nulls_for_each_entry_safe in htab batch ops (Yonghong Song)

Yonghong,
please review.