Re: [PATCH net-next v3 7/7] net: lan966x: Add support for XDP_REDIRECT

Alexander Lobakin
2022-11-22T12:04:47Z

From: Horatiu Vultur <horatiu.vultur@microchip.com>
Date: Mon, 21 Nov 2022 22:28:50 +0100

> Extend lan966x XDP support with the action XDP_REDIRECT. This is similar
> with the XDP_TX, so a lot of functionality can be reused.
>
> Signed-off-by: Horatiu Vultur <horatiu.vultur@microchip.com>
> ---
> .../ethernet/microchip/lan966x/lan966x_fdma.c | 83 +++++++++++++++----
> .../ethernet/microchip/lan966x/lan966x_main.c | 1 +
> .../ethernet/microchip/lan966x/lan966x_main.h | 10 ++-
> .../ethernet/microchip/lan966x/lan966x_xdp.c | 31 ++++++-
> 4 files changed, 109 insertions(+), 16 deletions(-)

[...]

> @@ -558,6 +575,10 @@ static int lan966x_fdma_napi_poll(struct napi_struct *napi, int weight)
> case FDMA_TX:
> lan966x_fdma_rx_advance_dcb(rx);
> continue;
> + case FDMA_REDIRECT:
> + lan966x_fdma_rx_advance_dcb(rx);
> + redirect = true;
> + continue;

I think you can save a couple lines here and avoid small code dup:

+ case FDMA_REDIRECT:
+ redirect = true;
+ fallthrough;
case FDMA_TX:
lan966x_fdma_rx_advance_dcb(rx);
continue;

The logics stays the same.

> case FDMA_DROP:
> lan966x_fdma_rx_free_page(rx);
> lan966x_fdma_rx_advance_dcb(rx);

[...]

> @@ -178,6 +180,7 @@ struct lan966x_tx_dcb_buf {
> struct net_device *dev;
> struct sk_buff *skb;
> struct xdp_frame *xdpf;
> + bool xdp_ndo;

I suggest carefully inspecting this struct with pahole (or by just
printkaying its layout/sizes/offsets at runtime) and see if there's
any holes and how it could be optimized.
Also, it's just my personal preference, but it's not that unpopular:
I don't trust bools inside structures as they may surprise with
their sizes or alignment depending on the architercture. Considering
all the blah I wrote, I'd define it as:

struct lan966x_tx_dcb_buf {
dma_addr_t dma_addr; // can be 8 bytes on 32-bit plat
struct net_device *dev; // ensure natural alignment
struct sk_buff *skb;
struct xdp_frame *xdpf;
u32 len;
u32 xdp_ndo:1; // put all your booleans here in
u32 used:1; // one u32
...
};

BTW, we usually do union { skb, xdpf } since they're mutually
exclusive. And to distinguish between XDP and regular Tx you can use
one more bit/bool. This can also come handy later when you add XSk
support (you will be adding it, right? Please :P).

> int len;
> dma_addr_t dma_addr;
> bool used;

[...]

> --
> 2.38.0

Thanks,
Olek