On Wed, 2020-11-18 at 16:15 +0800, Tian Tao wrote:
> use kmem_cache_zalloc instead kmem_cache_alloc and memset.
>
> Signed-off-by: Tian Tao <tiant...@hisilicon.com>
> ---
> net/core/skbuff.c | 10 +++-------
> 1 file changed, 3 insertions(+), 7 deletions(-)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index c9a5a3c..3449c1c 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -313,12 +313,10 @@ struct sk_buff *__build_skb(void *data, unsigned int
> frag_size)
> {
> struct sk_buff *skb;
>
> - skb = kmem_cache_alloc(skbuff_head_cache, GFP_ATOMIC);
> + skb = kmem_cache_zalloc(skbuff_head_cache, GFP_ATOMIC);
This will zeroed a slighly larger amount of data compared to the
existing code: offsetof(struct sk_buff, tail) == 182, sizeof(struct
sk_buff) == 224.
> if (unlikely(!skb))
> return NULL;
>
> - memset(skb, 0, offsetof(struct sk_buff, tail));
Additionally this leverages constant argument optimizations.
Possibly overall not noticeable, but this code path is quite critical
performance wise.
I would avoid the above.
> -
> return __build_skb_around(skb, data, frag_size);
> }
>
> @@ -6170,12 +6168,10 @@ static void *skb_ext_get_ptr(struct skb_ext *ext,
> enum skb_ext_id id)
> */
> struct skb_ext *__skb_ext_alloc(gfp_t flags)
> {
> - struct skb_ext *new = kmem_cache_alloc(skbuff_ext_cache, flags);
> + struct skb_ext *new = kmem_cache_zalloc(skbuff_ext_cache, flags);
>
> - if (new) {
> - memset(new->offset, 0, sizeof(new->offset));
Similar to the above, but additionally here the number of zeroed bytes
changes a lot and a few additional cachelines will be touched. The
performance impact is likely relevant.
Overall I think we should not do this.
Thanks,
Paolo
