This is a note to let you know that I've just added the patch titled net: stmmac: Fix overall budget calculation for rxtx_napi to the 5.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: net-stmmac-fix-overall-budget-calculation-for-rxtx_napi.patch and it can be found in the queue-5.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 81d0885d68ec427e62044cf46a400c9958ea0092 Mon Sep 17 00:00:00 2001 From: Song Yoong Siang <yoong.siang.song@xxxxxxxxx> Date: Fri, 3 Sep 2021 10:00:26 +0800 Subject: net: stmmac: Fix overall budget calculation for rxtx_napi From: Song Yoong Siang <yoong.siang.song@xxxxxxxxx> commit 81d0885d68ec427e62044cf46a400c9958ea0092 upstream. tx_done is not used for napi_complete_done(). Thus, NAPI busy polling mechanism by gro_flush_timeout and napi_defer_hard_irqs will not able be triggered after a packet is transmitted when there is no receive packet. Fix this by taking the maximum value between tx_done and rx_done as overall budget completed by the rxtx NAPI poll to ensure XDP Tx ZC operation is continuously polling for next Tx frame. This gives benefit of lower packet submission processing latency and jitter under XDP Tx ZC mode. Performance of tx-only using xdp-sock on Intel ADL-S platform is the same with and without this patch. root@intel-corei7-64:~# ./xdpsock -i enp0s30f4 -t -z -q 1 -n 10 sock0@enp0s30f4:1 txonly xdp-drv pps pkts 10.00 rx 0 0 tx 511630 8659520 sock0@enp0s30f4:1 txonly xdp-drv pps pkts 10.00 rx 0 0 tx 511625 13775808 sock0@enp0s30f4:1 txonly xdp-drv pps pkts 10.00 rx 0 0 tx 511619 18892032 Fixes: 132c32ee5bc0 ("net: stmmac: Add TX via XDP zero-copy socket") Cc: <stable@xxxxxxxxxxxxxxx> # 5.13.x Co-developed-by: Ong Boon Leong <boon.leong.ong@xxxxxxxxx> Signed-off-by: Ong Boon Leong <boon.leong.ong@xxxxxxxxx> Signed-off-by: Song Yoong Siang <yoong.siang.song@xxxxxxxxx> Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c @@ -5342,7 +5342,7 @@ static int stmmac_napi_poll_rxtx(struct struct stmmac_channel *ch = container_of(napi, struct stmmac_channel, rxtx_napi); struct stmmac_priv *priv = ch->priv_data; - int rx_done, tx_done; + int rx_done, tx_done, rxtx_done; u32 chan = ch->index; priv->xstats.napi_poll++; @@ -5352,14 +5352,16 @@ static int stmmac_napi_poll_rxtx(struct rx_done = stmmac_rx_zc(priv, budget, chan); + rxtx_done = max(tx_done, rx_done); + /* If either TX or RX work is not complete, return budget * and keep pooling */ - if (tx_done >= budget || rx_done >= budget) + if (rxtx_done >= budget) return budget; /* all work done, exit the polling mode */ - if (napi_complete_done(napi, rx_done)) { + if (napi_complete_done(napi, rxtx_done)) { unsigned long flags; spin_lock_irqsave(&ch->lock, flags); @@ -5370,7 +5372,7 @@ static int stmmac_napi_poll_rxtx(struct spin_unlock_irqrestore(&ch->lock, flags); } - return min(rx_done, budget - 1); + return min(rxtx_done, budget - 1); } /** Patches currently in stable-queue which might be from yoong.siang.song@xxxxxxxxx are queue-5.14/net-stmmac-fix-overall-budget-calculation-for-rxtx_napi.patch