Hi Konstantin,
On Fri, Mar 29, 2019 at 10:27:18AM +0000, Konstantin Ananyev wrote:
> Operations to set/update bit-fields often cause compilers
> to generate suboptimal code.
> To help avoid such situation for tx_offload fields:
> introduce new enum for tx_offload bit-fields lengths and offsets,
> and new function to generate raw tx_offload value.
>
> Signed-off-by: Konstantin Ananyev <konstantin.anan...@intel.com>
> Acked-by: Akhil Goyal <akhil.go...@nxp.com>
I understand the need. Out of curiosity, do you have any performance
numbers to share?
Few cosmetic questions below.
> ---
> lib/librte_mbuf/rte_mbuf.h | 79 ++++++++++++++++++++++++++++++++++----
> 1 file changed, 72 insertions(+), 7 deletions(-)
>
> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> index d961ccaf6..0b197e8ce 100644
> --- a/lib/librte_mbuf/rte_mbuf.h
> +++ b/lib/librte_mbuf/rte_mbuf.h
> @@ -479,6 +479,31 @@ struct rte_mbuf_sched {
> uint16_t reserved; /**< Reserved. */
> }; /**< Hierarchical scheduler */
>
> +/**
> + * enum for the tx_offload bit-fields lenghts and offsets.
> + * defines the layout of rte_mbuf tx_offload field.
> + */
> +enum {
> + RTE_MBUF_L2_LEN_BITS = 7,
> + RTE_MBUF_L3_LEN_BITS = 9,
> + RTE_MBUF_L4_LEN_BITS = 8,
> + RTE_MBUF_TSO_SEGSZ_BITS = 16,
> + RTE_MBUF_OUTL3_LEN_BITS = 9,
> + RTE_MBUF_OUTL2_LEN_BITS = 7,
> + RTE_MBUF_L2_LEN_OFS = 0,
> + RTE_MBUF_L3_LEN_OFS = RTE_MBUF_L2_LEN_OFS + RTE_MBUF_L2_LEN_BITS,
> + RTE_MBUF_L4_LEN_OFS = RTE_MBUF_L3_LEN_OFS + RTE_MBUF_L3_LEN_BITS,
> + RTE_MBUF_TSO_SEGSZ_OFS = RTE_MBUF_L4_LEN_OFS + RTE_MBUF_L4_LEN_BITS,
> + RTE_MBUF_OUTL3_LEN_OFS =
> + RTE_MBUF_TSO_SEGSZ_OFS + RTE_MBUF_TSO_SEGSZ_BITS,
> + RTE_MBUF_OUTL2_LEN_OFS =
> + RTE_MBUF_OUTL3_LEN_OFS + RTE_MBUF_OUTL3_LEN_BITS,
> + RTE_MBUF_TXOFLD_UNUSED_OFS =
> + RTE_MBUF_OUTL2_LEN_OFS + RTE_MBUF_OUTL2_LEN_BITS,
> + RTE_MBUF_TXOFLD_UNUSED_BITS =
> + sizeof(uint64_t) * CHAR_BIT - RTE_MBUF_TXOFLD_UNUSED_OFS,
> +};
> +
What is the advantage of defining an enum instead of #defines?
In any case, I wonder if it wouldn't be clearer to change the order like
this:
enum {
RTE_MBUF_L2_LEN_OFS = 0,
RTE_MBUF_L2_LEN_BITS = 7,
RTE_MBUF_L3_LEN_OFS = RTE_MBUF_L2_LEN_OFS + RTE_MBUF_L2_LEN_BITS,
RTE_MBUF_L3_LEN_BITS = 9,
RTE_MBUF_L4_LEN_OFS = RTE_MBUF_L3_LEN_OFS + RTE_MBUF_L3_LEN_BITS,
RTE_MBUF_L4_LEN_BITS = 8,
...
> /**
> * The generic rte_mbuf, containing a packet mbuf.
> */
> @@ -640,19 +665,24 @@ struct rte_mbuf {
> uint64_t tx_offload; /**< combined for easy fetch */
> __extension__
> struct {
> - uint64_t l2_len:7;
> + uint64_t l2_len:RTE_MBUF_L2_LEN_BITS;
> /**< L2 (MAC) Header Length for non-tunneling pkt.
> * Outer_L4_len + ... + Inner_L2_len for tunneling pkt.
> */
> - uint64_t l3_len:9; /**< L3 (IP) Header Length. */
> - uint64_t l4_len:8; /**< L4 (TCP/UDP) Header Length. */
> - uint64_t tso_segsz:16; /**< TCP TSO segment size */
> + uint64_t l3_len:RTE_MBUF_L3_LEN_BITS;
> + /**< L3 (IP) Header Length. */
> + uint64_t l4_len:RTE_MBUF_L4_LEN_BITS;
> + /**< L4 (TCP/UDP) Header Length. */
> + uint64_t tso_segsz:RTE_MBUF_TSO_SEGSZ_BITS;
> + /**< TCP TSO segment size */
>
> /* fields for TX offloading of tunnels */
> - uint64_t outer_l3_len:9; /**< Outer L3 (IP) Hdr Length.
> */
> - uint64_t outer_l2_len:7; /**< Outer L2 (MAC) Hdr
> Length. */
> + uint64_t outer_l3_len:RTE_MBUF_OUTL3_LEN_BITS;
> + /**< Outer L3 (IP) Hdr Length. */
> + uint64_t outer_l2_len:RTE_MBUF_OUTL2_LEN_BITS;
> + /**< Outer L2 (MAC) Hdr Length. */
>
> - /* uint64_t unused:8; */
> + /* uint64_t unused:RTE_MBUF_TXOFLD_UNUSED_BITS; */
> };
> };
>
> @@ -2243,6 +2273,41 @@ static inline int rte_pktmbuf_chain(struct rte_mbuf
> *head, struct rte_mbuf *tail
> return 0;
> }
>
> +/*
> + * @warning
> + * @b EXPERIMENTAL: This API may change without prior notice.
> + *
> + * For given input values generate raw tx_offload value.
> + * @param il2
> + * l2_len value.
> + * @param il3
> + * l3_len value.
> + * @param il4
> + * l4_len value.
> + * @param tso
> + * tso_segsz value.
> + * @param ol3
> + * outer_l3_len value.
> + * @param ol2
> + * outer_l2_len value.
> + * @param unused
> + * unused value.
> + * @return
> + * raw tx_offload value.
> + */
> +static __rte_always_inline uint64_t
> +rte_mbuf_tx_offload(uint64_t il2, uint64_t il3, uint64_t il4, uint64_t tso,
> + uint64_t ol3, uint64_t ol2, uint64_t unused)
> +{
> + return il2 << RTE_MBUF_L2_LEN_OFS |
> + il3 << RTE_MBUF_L3_LEN_OFS |
> + il4 << RTE_MBUF_L4_LEN_OFS |
> + tso << RTE_MBUF_TSO_SEGSZ_OFS |
> + ol3 << RTE_MBUF_OUTL3_LEN_OFS |
> + ol2 << RTE_MBUF_OUTL2_LEN_OFS |
> + unused << RTE_MBUF_TXOFLD_UNUSED_OFS;
> +}
> +
> /**
>From what I see, the problem is quite similar to what was done with
rte_mbuf_sched_set() recently. So I wondered if it was possible to
declare a structure like this:
struct rte_mbuf_ol_len {
uint64_t l2_len:7;
uint64_t l3_len:9; /**< L3 (IP) Header Length. */
uint64_t l4_len:8; /**< L4 (TCP/UDP) Header Length. */
...
}
And have the set function like this:
m->l = (struct rte_mbuf_ol_len) {
.l2_len = l2_len,
.l3_len = l3_len,
.l4_len = l4_len,
...
This would avoid the definition of the offsets and bits, but I didn't
find any way to declare these fields as anonymous in the mbuf structure.
Did you tried that way too?
Thanks,
Olivier
