On Mittwoch, 24. Januar 2018 12:21:37 CET Matthias Schiffer wrote: > NIC drivers generally try to ensure that the "network header" is aligned > to a 4-byte boundary. This is not always possible: When Ethernet frames are > encapsulated in other packets with 4-byte aligned headers, the inner > Ethernet header will have 4-byte alignment, and in consequence, the inner > network header is aligned to 2, but not to 4 bytes. > > Most parts of batman-adv only care about 2-byte alignment; in particular, > no unaligned accesses occur in performance-critical paths that handle > actual payload data. This is not true for OGM handling: the seqno and crc > fields are accessed as 32-bit values. To avoid these unaligned accesses, > this patch reduces the expected packet alignment to 2 bytes for all of > batadv's packet types. > > As no unaligned accesses existed on the performance-critical paths anyways, > this chance does have any (positive or negative) effect on performance, but > it still makes sense to avoid these accesses to prevent log noise when > examining other unaligned accesses in the kernel while batman-adv is > active. > > Signed-off-by: Matthias Schiffer <mschif...@universe-factory.net> > --- > include/uapi/linux/batadv_packet.h | 13 ++----------- > 1 file changed, 2 insertions(+), 11 deletions(-)
I know your intentions and I understand the problem. But there is the chance
that David Miller will reject this patch - like he did it some years ago
with a similar (not the same) patch:
"I'm not applying this, please try work to implement this more
acceptably first." [1]
But maybe he has now some other opinion because the unaligned problem is
caused by the encapsulation in VXLAN or maybe he has a better idea. At
least VXLAN encap stuff should affect a lot more net code than batman-adv.
Kind regards,
Sven
[1] https://patchwork.ozlabs.org/patch/295596/
>
> diff --git a/include/uapi/linux/batadv_packet.h
> b/include/uapi/linux/batadv_packet.h
> index daefd728..894d8d2f 100644
> --- a/include/uapi/linux/batadv_packet.h
> +++ b/include/uapi/linux/batadv_packet.h
> @@ -196,8 +196,6 @@ struct batadv_bla_claim_dst {
> __be16 group; /* group id */
> };
>
> -#pragma pack()
> -
> /**
> * struct batadv_ogm_packet - ogm (routing protocol) packet
> * @packet_type: batman-adv packet type, part of the general header
> @@ -222,9 +220,6 @@ struct batadv_ogm_packet {
> __u8 reserved;
> __u8 tq;
> __be16 tvlv_len;
> - /* __packed is not needed as the struct size is divisible by 4,
> - * and the largest data type in this struct has a size of 4.
> - */
> };
>
> #define BATADV_OGM_HLEN sizeof(struct batadv_ogm_packet)
> @@ -249,9 +244,6 @@ struct batadv_ogm2_packet {
> __u8 orig[ETH_ALEN];
> __be16 tvlv_len;
> __be32 throughput;
> - /* __packed is not needed as the struct size is divisible by 4,
> - * and the largest data type in this struct has a size of 4.
> - */
> };
>
> #define BATADV_OGM2_HLEN sizeof(struct batadv_ogm2_packet)
> @@ -405,7 +397,6 @@ struct batadv_icmp_packet_rr {
> * misalignment of the payload after the ethernet header. It may also lead to
> * leakage of information when the padding it not initialized before sending.
> */
> -#pragma pack(2)
>
> /**
> * struct batadv_unicast_packet - unicast packet for network payload
> @@ -533,8 +524,6 @@ struct batadv_coded_packet {
> __be16 coded_len;
> };
>
> -#pragma pack()
> -
> /**
> * struct batadv_unicast_tvlv_packet - generic unicast packet with tvlv
> payload
> * @packet_type: batman-adv packet type, part of the general header
> @@ -641,4 +630,6 @@ struct batadv_tvlv_mcast_data {
> __u8 reserved[3];
> };
>
> +#pragma pack()
> +
> #endif /* _UAPI_LINUX_BATADV_PACKET_H_ */
>
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