netdev - Re: [PATCH net-next 5/5] tsnep: Add XDP socket zero-copy TX support

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Message-ID: <ZCtU8WN+NpNXS+N8@boxer>
Date:   Tue, 4 Apr 2023 00:36:33 +0200
From:   Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To:     Gerhard Engleder <gerhard@...leder-embedded.com>
CC:     <netdev@...r.kernel.org>, <bpf@...r.kernel.org>,
        <davem@...emloft.net>, <kuba@...nel.org>, <edumazet@...gle.com>,
        <pabeni@...hat.com>, <bjorn@...nel.org>,
        <magnus.karlsson@...el.com>, <jonathan.lemon@...il.com>
Subject: Re: [PATCH net-next 5/5] tsnep: Add XDP socket zero-copy TX support

On Sun, Apr 02, 2023 at 09:38:38PM +0200, Gerhard Engleder wrote:
> Send and complete XSK pool frames within TX NAPI context. NAPI context
> is triggered by ndo_xsk_wakeup.
> 
> Signed-off-by: Gerhard Engleder <gerhard@...leder-embedded.com>
> ---
>  drivers/net/ethernet/engleder/tsnep.h      |   2 +
>  drivers/net/ethernet/engleder/tsnep_main.c | 131 +++++++++++++++++++--
>  2 files changed, 123 insertions(+), 10 deletions(-)
> 

(...)

> +static void tsnep_xdp_xmit_zc(struct tsnep_tx *tx)
> +{
> +	int desc_available = tsnep_tx_desc_available(tx);
> +	struct xdp_desc xdp_desc;
> +	bool xmit = false;
> +
> +	/* ensure that TX ring is not filled up by XDP, always MAX_SKB_FRAGS
> +	 * will be available for normal TX path and queue is stopped there if
> +	 * necessary
> +	 */
> +	if (desc_available <= (MAX_SKB_FRAGS + 1))
> +		return;
> +	desc_available -= MAX_SKB_FRAGS + 1;
> +
> +	while (xsk_tx_peek_desc(tx->xsk_pool, &xdp_desc) && desc_available--) {

Again, I am curious how batch API usage would improve your perf.

> +		tsnep_xdp_xmit_frame_ring_zc(&xdp_desc, tx);
> +		xmit = true;
> +	}
> +
> +	if (xmit) {
> +		tsnep_xdp_xmit_flush(tx);
> +		xsk_tx_release(tx->xsk_pool);
> +	}
> +}
> +