On 16/05/2023 14.37, Alexander Lobakin wrote:
From: Larysa Zaremba<larysa.zaremba@xxxxxxxxx>
Date: Mon, 15 May 2023 19:08:39 +0200
On Mon, May 15, 2023 at 06:17:02PM +0200, Jesper Dangaard Brouer wrote:
On 12/05/2023 17.26, Larysa Zaremba wrote:
From: Aleksander Lobakin<aleksander.lobakin@xxxxxxxxx>
When using XDP hints, metadata sometimes has to be much bigger
than 32 bytes. Relax the restriction, allow metadata larger than 32 bytes
and make __skb_metadata_differs() work with bigger lengths.
Now size of metadata is only limited by the fact it is stored as u8
in skb_shared_info, so maximum possible value is 255.
>>>
I'm confused, IIRC the metadata area isn't stored "in skb_shared_info".
The maximum possible size is limited by the XDP headroom, which is also
shared/limited with/by xdp_frame. I must be reading the sentence wrong,
somehow.
>
skb_shared_info::meta_size is u8. Since metadata gets carried from
xdp_buff to skb, this check is needed (it's compile-time constant anyway).
Check for headroom is done separately already (two sentences below).
Damn, argh, for SKBs the "meta_len" is stored in skb_shared_info, which
is located on another cacheline.
That is a sure way to KILL performance! :-(
But only use for SKBs that gets created from xdp with metadata, right?
It's not 'metadata is stored as u8', it's 'metadata size is stored as u8' :)
Maybe I should rephrase it better in v2.
Yes, a rephrase will be good.
--Jesper
static inline u8 skb_metadata_len(const struct sk_buff *skb)
{
return skb_shinfo(skb)->meta_len;
}
