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Date: Mon, 29 Jul 2019 18:16:12 +0200 From: Jesper Dangaard Brouer <brouer@...hat.com> To: Toke Høiland-Jørgensen <toke@...hat.com> Cc: Daniel Borkmann <daniel@...earbox.net>, Alexei Starovoitov <ast@...nel.org>, netdev@...r.kernel.org, David Miller <davem@...emloft.net>, Jakub Kicinski <jakub.kicinski@...ronome.com>, Björn Töpel <bjorn.topel@...il.com>, Yonghong Song <yhs@...com>, brouer@...hat.com Subject: Re: [PATCH bpf-next v5 3/6] xdp: Add devmap_hash map type for looking up devices by hashed index On Fri, 26 Jul 2019 18:06:55 +0200 Toke Høiland-Jørgensen <toke@...hat.com> wrote: > From: Toke Høiland-Jørgensen <toke@...hat.com> > > A common pattern when using xdp_redirect_map() is to create a device map > where the lookup key is simply ifindex. Because device maps are arrays, > this leaves holes in the map, and the map has to be sized to fit the > largest ifindex, regardless of how many devices actually are actually > needed in the map. > > This patch adds a second type of device map where the key is looked up > using a hashmap, instead of being used as an array index. This allows maps > to be densely packed, so they can be smaller. > > Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com> > Acked-by: Yonghong Song <yhs@...com> Acked-by: Jesper Dangaard Brouer <brouer@...hat.com> [...] > +static inline struct hlist_head *dev_map_index_hash(struct bpf_dtab *dtab, > + int idx) > +{ > + return &dtab->dev_index_head[idx & (dtab->n_buckets - 1)]; > +} I was about to complain about, that you are not using a pre-calculated MASK value, instead of doing the -1 operation each time. But I looked at the ASM code, and the LEA operation used does the -1 operation in the same instruction, so I guess this makes no performance difference. -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
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