Messages in this thread | | | From | Jesper Dangaard Brouer <> | Date | Tue, 16 May 2023 17:35:27 +0200 | Subject | Re: [PATCH RESEND bpf-next 14/15] net, xdp: allow metadata > 32 |
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On 16/05/2023 14.37, Alexander Lobakin wrote: > From: Larysa Zaremba<larysa.zaremba@intel.com> > 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@intel.com> >>>> >>>> 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; }
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