need definitions / references

[fwefew 4t4tg]

Mr. Hemminger,

Thank you once again for your help.

Now, I did see the one-liner DPDK puts in code which you reference:

struct rte_eth_thresh {
        uint8_t pthresh; /**< Ring prefetch threshold. */
        uint8_t hthresh; /**< Ring host threshold. */
        uint8_t wthresh; /**< Ring writeback threshold. */
};

The problem for me is I don't know what "ring host threshold" or "ring
writeback" means.

"Ring prefetch threshold" I think I understand. This refers to how mbufs
are pending in the ring before it starts writing them onto the wire. This
seems to have some connection to tx_rs_thresh.

On Thu, Mar 17, 2022 at 12:48 PM Stephen Hemminger <
stephen at networkplumber.org> wrote:

> On Thu, 17 Mar 2022 12:05:33 -0400
> fwefew 4t4tg <7532yahoo at gmail.com> wrote:
>
> > DPDK provides but does not define (that I can see at least) these TXQ
> > config fields. What are these fields what do they do?
> >
> > https://doc.dpdk.org/api/structrte__eth__thresh.html
> > uint8_t pthresh
> > uint8_t hthresh
> > uint8_t wthresh
>
> These are low level details inherited from original Intel NIC's (ie ixgbe)
> they only apply to some NICs. They are used to control the ring threshold
> values relating to PCI.
>
> In rte_ethdev.h
> /**
>  * A structure used to configure the ring threshold registers of an Rx/Tx
>  * queue for an Ethernet port.
>  */
> struct rte_eth_thresh {
>         uint8_t pthresh; /**< Ring prefetch threshold. */
>         uint8_t hthresh; /**< Ring host threshold. */
>         uint8_t wthresh; /**< Ring writeback threshold. */
> };
>
>
> > And here: What is the RS bit?
> > https://doc.dpdk.org/api/structrte__eth__txconf.html
> > uint16_t tx_rs_thresh.
>
> Ready to Send?
>
> >
> > And some what unrelated: What is a ``doorbell"? this is something I
> > continue to run into esp. in Mellanox NIC papers? Doorbell counts are
> > reported for AWS NICs at least with xstats api:
> >
> > tx_q0_doorbells: 18812
> > tx_q1_doorbells: 18861
>
> These are how many times driver needed to poke hardware to tell it
> that new packets are ready to send.
>
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