netdev - [RFC net-next 1/4] net: napi threaded: remove unnecessary locking

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Message-Id: <20211210193556.1349090-2-yannick.vignon@oss.nxp.com>
Date:   Fri, 10 Dec 2021 20:35:53 +0100
From:   Yannick Vignon <yannick.vignon@....nxp.com>
To:     Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        netdev@...r.kernel.org, Ong Boon Leong <boon.leong.ong@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jose Abreu <joabreu@...opsys.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Wei Wang <weiwan@...gle.com>,
        Alexander Lobakin <alexandr.lobakin@...el.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Xiaoliang Yang <xiaoliang.yang_1@....com>, mingkai.hu@....com,
        Joakim Zhang <qiangqing.zhang@....com>,
        sebastien.laveze@....com
Cc:     Yannick Vignon <yannick.vignon@....com>
Subject: [RFC net-next 1/4] net: napi threaded: remove unnecessary locking

From: Yannick Vignon <yannick.vignon@....com>

NAPI polling is normally protected by local_bh_disable()/local_bh_enable()
calls, to avoid that code from being executed concurrently due to the
softirq design. When NAPI instances are assigned their own dedicated kernel
thread however, that concurrent code execution can no longer happen.

Removing the lock helps lower latencies when handling real-time traffic
(whose processing could still be delayed because of on-going processing of
best-effort traffic), and should also have a positive effect on overall
performance.

Signed-off-by: Yannick Vignon <yannick.vignon@....com>
---
 net/core/dev.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 15ac064b5562..e35d90e70c75 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -7131,13 +7131,11 @@ static int napi_threaded_poll(void *data)
 		for (;;) {
 			bool repoll = false;
 
-			local_bh_disable();
 
 			have = netpoll_poll_lock(napi);
 			__napi_poll(napi, &repoll);
 			netpoll_poll_unlock(have);
 
-			local_bh_enable();
 
 			if (!repoll)
 				break;
-- 
2.25.1