netdev - [PATCH net-next 5/5] net: optimize napi_threaded

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Date:   Fri, 21 Apr 2023 09:43:57 +0000
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com,
        Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net-next 5/5] net: optimize napi_threaded_poll() vs RPS/RFS

We use napi_threaded_poll() in order to reduce our softirq dependency.

We can add a followup of 821eba962d95 ("net: optimize napi_schedule_rps()")
to further remove the need of firing NET_RX_SOFTIRQ whenever
RPS/RFS are used.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/linux/netdevice.h |  3 +++
 net/core/dev.c            | 12 ++++++++++--
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index a6a3e9457d6cbc9fcbbde96b43b4b21878495403..08fbd4622ccf731daaee34ad99773d6dc2e82fa6 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3194,7 +3194,10 @@ struct softnet_data {
 #ifdef CONFIG_RPS
 	struct softnet_data	*rps_ipi_list;
 #endif
+
 	bool			in_net_rx_action;
+	bool			in_napi_threaded_poll;
+
 #ifdef CONFIG_NET_FLOW_LIMIT
 	struct sd_flow_limit __rcu *flow_limit;
 #endif
diff --git a/net/core/dev.c b/net/core/dev.c
index 7d9ec23f97c6ec80ec9f971f740a9da747f78ceb..735096d42c1d13999597a882370ca439e9389e24 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4603,10 +4603,10 @@ static void napi_schedule_rps(struct softnet_data *sd)
 		sd->rps_ipi_next = mysd->rps_ipi_list;
 		mysd->rps_ipi_list = sd;
 
-		/* If not called from net_rx_action()
+		/* If not called from net_rx_action() or napi_threaded_poll()
 		 * we have to raise NET_RX_SOFTIRQ.
 		 */
-		if (!mysd->in_net_rx_action)
+		if (!mysd->in_net_rx_action && !mysd->in_napi_threaded_poll)
 			__raise_softirq_irqoff(NET_RX_SOFTIRQ);
 		return;
 	}
@@ -6631,11 +6631,19 @@ static int napi_threaded_poll(void *data)
 
 			local_bh_disable();
 			sd = this_cpu_ptr(&softnet_data);
+			sd->in_napi_threaded_poll = true;
 
 			have = netpoll_poll_lock(napi);
 			__napi_poll(napi, &repoll);
 			netpoll_poll_unlock(have);
 
+			sd->in_napi_threaded_poll = false;
+			barrier();
+
+			if (sd_has_rps_ipi_waiting(sd)) {
+				local_irq_disable();
+				net_rps_action_and_irq_enable(sd);
+			}
 			skb_defer_free_flush(sd);
 			local_bh_enable();
 
-- 
2.40.0.634.g4ca3ef3211-goog