[dpdk-dev] rte_mbuf structure size in Windows
Tal Shnaiderman
talshn at mellanox.com
Wed May 13 09:55:07 CEST 2020
Hi,
I've noticed that there is a difference between the size of rte_mbuf in a Unix build comparing to Windows.
The requirements is for rte_mbuf is to be RTE_CACHE_LINE_MIN_SIZE * 2 bytes however when I'm building it in Windows the size is RTE_CACHE_LINE_MIN_SIZE * 3.
Looks like the diff results from the usage of bit fields inside rte_mbuf, from my testing it looks to me like the usage of 2 different bit fielded types inside rte_mbuf causes additional padding in Windows.
For example from rte_mbuf, the following unions have the same size in Windows and Linux:
union {
uint32_t packet_type;
// bit fields of type uint32_t will follow
...
};...
4 bytes both in Unix and Windows.
union {
uint64_t tx_offload;
// bit fields of type uint64_t will follow
...
};
8 bytes both in Unix and Windows.
However when creating a struct containing both unions I'm getting sizeof 16 bytes in Unix and 24 bytes in Windows.
Did someone faced this issue before? Is this a result of different alignment between gcc and clang when bit fields are used?
Thanks,
Tal
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