[PATCH net 1/1] net: stmmac: Fix overall budget calculation for rxtx_napi

[PATCH net 1/1] net: stmmac: Fix overall budget calculation for rxtx_napi

[Song Yoong Siang]

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@vger.kernel.org> # 5.13.x
Co-developed-by: Ong Boon Leong <boon.leong.ong@intel.com>
Signed-off-by: Ong Boon Leong <boon.leong.ong@intel.com>
Signed-off-by: Song Yoong Siang <yoong.siang.song@intel.com>
---
 drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index ed0cd3920171..97238359e101 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -5347,7 +5347,7 @@ static int stmmac_napi_poll_rxtx(struct napi_struct *napi, int budget)
 	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++;
@@ -5357,14 +5357,16 @@ static int stmmac_napi_poll_rxtx(struct napi_struct *napi, int budget)
 
 	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);
@@ -5375,7 +5377,7 @@ static int stmmac_napi_poll_rxtx(struct napi_struct *napi, int budget)
 		spin_unlock_irqrestore(&ch->lock, flags);
 	}
 
-	return min(rx_done, budget - 1);
+	return min(rxtx_done, budget - 1);
 }
 
 /**
-- 
2.25.1

Re: [PATCH net 1/1] net: stmmac: Fix overall budget calculation for rxtx_napi

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (refs/heads/master):

On Fri,  3 Sep 2021 10:00:26 +0800 you wrote:
> 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.
> 
> [...]

Here is the summary with links:
  - [net,1/1] net: stmmac: Fix overall budget calculation for rxtx_napi
    https://git.kernel.org/netdev/net/c/81d0885d68ec

You are awesome, thank you!
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