From: Stefan Sperling <stsp@stsp.name>
Subject: Re: Use SoftLRO in em(4)
To: Jan Klemkow <jan@openbsd.org>
Cc: tech@openbsd.org
Date: Tue, 11 Nov 2025 15:05:02 +0100

On Tue, Nov 04, 2025 at 01:27:20PM +0100, Jan Klemkow wrote:
> Hi,
> 
> This diff adds the use of SoftLRO in em(4).
> 
> It uses the E1000_RXD_STAT_TCPCS and E1000_RXD_STAT_UDPCS flags to
> distinguish between TCP and non-TCP packets.  Both flags are set on UDP
> packets and just E1000_RXD_STAT_TCPCS and TCP ones.  Thus, I ended up
> with the TCP and !UDP logic below.
> 
> More tests especially on older hardware are welcome.
> 
> I tested it with:
> em0 at pci2 dev 0 function 0 "Intel I210" rev 0x03: msi, address a8:a1:59:f2:a4:81
> em1 at pci3 dev 0 function 0 "Intel I210" rev 0x03: msi, address a8:a1:59:f2:a4:82
> 
> ok?
> 
> bye,
> Jan

Hi Jan,

This diff breaks the RAMDISK_CD build:

  ld: error: undefined symbol: tcp_softlro_glue
  >>> referenced by if_em.c:3196 (/usr/src/sys/dev/pci/if_em.c:3196)
  >>>               if_em.o:(em_rxeof)

Looks like some more ifndef SMALL will be needed.

> Index: dev/pci/if_em.c
> ===================================================================
> RCS file: /cvs/src/sys/dev/pci/if_em.c,v
> diff -u -p -r1.379 if_em.c
> --- dev/pci/if_em.c	14 Jul 2025 11:52:43 -0000	1.379
> +++ dev/pci/if_em.c	4 Nov 2025 10:24:35 -0000
> @@ -2013,6 +2013,9 @@ em_setup_interface(struct em_softc *sc)
>  		ifp->if_capabilities |= IFCAP_TSOv4 | IFCAP_TSOv6;
>  	}
>  
> +	ifp->if_capabilities |= IFCAP_LRO;
> +	ifp->if_xflags |= IFXF_LRO;
> +
>  	/* 
>  	 * Specify the media types supported by this adapter and register
>  	 * callbacks to update media and link information
> @@ -3066,12 +3069,13 @@ em_rxeof(struct em_queue *que)
>  {
>  	struct em_softc	    *sc = que->sc;
>  	struct ifnet	    *ifp = &sc->sc_ac.ac_if;
> +	struct mbuf_list    mltcp = MBUF_LIST_INITIALIZER();
>  	struct mbuf_list    ml = MBUF_LIST_INITIALIZER();
>  	struct mbuf	    *m;
>  	u_int8_t	    accept_frame = 0;
>  	u_int8_t	    eop = 0;
>  	u_int16_t	    len, desc_len, prev_len_adj;
> -	int		    i, rv = 0;
> +	int		    i, rv = 0, livelocked = 0;
>  
>  	/* Pointer to the receive descriptor being examined. */
>  	struct em_rx_desc   *desc;
> @@ -3186,7 +3190,12 @@ em_rxeof(struct em_queue *que)
>  					m->m_flags |= M_VLANTAG;
>  				}
>  #endif
> -				ml_enqueue(&ml, m);
> +				if (ISSET(ifp->if_xflags, IFXF_LRO) &&
> +				    desc->status & E1000_RXD_STAT_TCPCS &&
> +				    !(desc->status & E1000_RXD_STAT_UDPCS))
> +					tcp_softlro_glue(&mltcp, m, ifp);
> +				else
> +					ml_enqueue(&ml, m);
>  
>  				que->rx.fmp = NULL;
>  				que->rx.lmp = NULL;
> @@ -3214,7 +3223,11 @@ em_rxeof(struct em_queue *que)
>  
>  	que->rx.sc_rx_desc_tail = i;
>  
> +	if (ifiq_input(&ifp->if_rcv, &mltcp))
> +		livelocked = 1;
>  	if (ifiq_input(&ifp->if_rcv, &ml))
> +		livelocked = 1;
> +	if (livelocked)
>  		if_rxr_livelocked(&que->rx.sc_rx_ring);
>  
>  	return (rv);
> 
>