netdev - Re: [RFC PATCH bpf-next 1/3] bpf: factor out helpers for htab bucket and element lookup

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Date:   Tue, 21 Dec 2021 11:32:05 -0800
From:   Yonghong Song <yhs@...com>
To:     Hou Tao <houtao1@...wei.com>, Alexei Starovoitov <ast@...nel.org>
CC:     Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, <netdev@...r.kernel.org>,
        <bpf@...r.kernel.org>, <yunbo.xufeng@...ux.alibaba.com>
Subject: Re: [RFC PATCH bpf-next 1/3] bpf: factor out helpers for htab bucket
 and element lookup



On 12/18/21 9:22 PM, Hou Tao wrote:
> Call to htab_map_hash() and element lookup (e.g. lookup_elem_raw())
> are scattered all over the place. In order to make the change of hash
> algorithm and element comparison logic easy, factor out three helpers
> correspondinging to three lookup patterns in htab imlementation:
> 
> 1) lookup element locklessly by key (e.g. htab_map_lookup_elem)
> nolock_lookup_elem()
> 2) lookup element with bucket locked (e.g. htab_map_delete_elem)
> lock_lookup_elem()
> 3) lookup bucket and lock it later (e.g. htab_map_update_elem)
> lookup_bucket()
> 
> For performance reason, mark these three helpers as always_inline.
> 
> Also factor out two helpers: next_elem() and first_elem() to
> make the iteration of element list more concise.
> 
> Signed-off-by: Hou Tao <houtao1@...wei.com>
> ---
>   kernel/bpf/hashtab.c | 350 ++++++++++++++++++++++---------------------
>   1 file changed, 183 insertions(+), 167 deletions(-)
> 
> diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
> index d29af9988f37..e21e27162e08 100644
> --- a/kernel/bpf/hashtab.c
> +++ b/kernel/bpf/hashtab.c
> @@ -127,6 +127,23 @@ struct htab_elem {
>   	char key[] __aligned(8);
>   };
>   
> +struct nolock_lookup_elem_result {
> +	struct htab_elem *elem;
> +	u32 hash;
> +};
> +
> +struct lock_lookup_elem_result {
> +	struct bucket *bucket;
> +	unsigned long flags;
> +	struct htab_elem *elem;
> +	u32 hash;
> +};
> +
> +struct lookup_bucket_result {
> +	struct bucket *bucket;
> +	u32 hash;
> +};
> +
>   static inline bool htab_is_prealloc(const struct bpf_htab *htab)
>   {
>   	return !(htab->map.map_flags & BPF_F_NO_PREALLOC);
> @@ -233,6 +250,22 @@ static bool htab_has_extra_elems(struct bpf_htab *htab)
>   	return !htab_is_percpu(htab) && !htab_is_lru(htab);
>   }
>   
> +static inline struct htab_elem *next_elem(const struct htab_elem *e)
> +{
> +	struct hlist_nulls_node *n =
> +		rcu_dereference_raw(hlist_nulls_next_rcu(&e->hash_node));
> +
> +	return hlist_nulls_entry_safe(n, struct htab_elem, hash_node);
> +}
> +
> +static inline struct htab_elem *first_elem(const struct hlist_nulls_head *head)
> +{
> +	struct hlist_nulls_node *n =
> +		rcu_dereference_raw(hlist_nulls_first_rcu(head));
> +
> +	return hlist_nulls_entry_safe(n, struct htab_elem, hash_node);
> +}
> +
>   static void htab_free_prealloced_timers(struct bpf_htab *htab)
>   {
>   	u32 num_entries = htab->map.max_entries;
> @@ -614,6 +647,59 @@ static struct htab_elem *lookup_nulls_elem_raw(struct hlist_nulls_head *head,
>   	return NULL;
>   }
>   
> +static __always_inline void
> +nolock_lookup_elem(struct bpf_htab *htab, void *key,
> +		   struct nolock_lookup_elem_result *e)

There is no need to mark such (non-trivial) functions as 
__always_inline. Let compiler decide whether inlining
should be done or not.


> +{
> +	struct hlist_nulls_head *head;
> +	u32 key_size, hash;
> +
> +	key_size = htab->map.key_size;
> +	hash = htab_map_hash(key, key_size, htab->hashrnd);
> +	head = select_bucket(htab, hash);
> +
> +	e->elem = lookup_nulls_elem_raw(head, hash, key, key_size,
> +					htab->n_buckets);
> +	e->hash = hash;
> +}
> +
> +static __always_inline void
> +lock_lookup_elem(struct bpf_htab *htab, void *key,
> +		 struct lock_lookup_elem_result *e)
[...]