netdev - [RFC PATCH net-next 4/6] net: modify kthread handler to use __napi

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Message-Id: <20200914172453.1833883-5-weiwan@google.com>
Date:   Mon, 14 Sep 2020 10:24:51 -0700
From:   Wei Wang <weiwan@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>,
        Felix Fietkau <nbd@....name>, Wei Wang <weiwan@...gle.com>
Subject: [RFC PATCH net-next 4/6] net: modify kthread handler to use __napi_poll()

From: Jakub Kicinski <kuba@...nel.org> 

The current kthread handler calls napi_poll() and has to pass a dummy
repoll list to the function, which seems redundent. The new proposed
kthread handler calls the newly proposed __napi_poll(), and respects
napi->weight as before. If repoll is needed, cond_resched() is called
first to give other tasks a chance to run before repolling.
This change is proposed by Jakub Kicinski <kuba@...nel.org> on top of
the previous patch.

Signed-off-by: Jakub Kicinski <kuba@...nel.org>
Signed-off-by: Wei Wang <weiwan@...gle.com>
---
 net/core/dev.c | 62 +++++++++++++++++++-------------------------------
 1 file changed, 24 insertions(+), 38 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index bc2a7681b239..be676c21bdc4 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6763,6 +6763,15 @@ static int __napi_poll(struct napi_struct *n, bool *repoll)
 
 	gro_normal_list(n);
 
+	/* Some drivers may have called napi_schedule
+	 * prior to exhausting their budget.
+	 */
+	if (unlikely(!list_empty(&n->poll_list))) {
+		pr_warn_once("%s: Budget exhausted after napi rescheduled\n",
+			     n->dev ? n->dev->name : "backlog");
+		return work;
+	}
+
 	*repoll = true;
 
 	return work;
@@ -6783,15 +6792,6 @@ static int napi_poll(struct napi_struct *n, struct list_head *repoll)
 	if (!do_repoll)
 		goto out_unlock;
 
-	/* Some drivers may have called napi_schedule
-	 * prior to exhausting their budget.
-	 */
-	if (unlikely(!list_empty(&n->poll_list))) {
-		pr_warn_once("%s: Budget exhausted after napi rescheduled\n",
-			     n->dev ? n->dev->name : "backlog");
-		goto out_unlock;
-	}
-
 	list_add_tail(&n->poll_list, repoll);
 
 out_unlock:
@@ -6820,40 +6820,26 @@ static int napi_thread_wait(struct napi_struct *napi)
 static int napi_threaded_poll(void *data)
 {
 	struct napi_struct *napi = data;
+	void *have;
 
 	while (!napi_thread_wait(napi)) {
-		struct list_head dummy_repoll;
-		int budget = netdev_budget;
-		unsigned long time_limit;
-		bool again = true;
+		for (;;) {
+			bool repoll = false;
 
-		INIT_LIST_HEAD(&dummy_repoll);
-		local_bh_disable();
-		time_limit = jiffies + 2;
-		do {
-			/* ensure that the poll list is not empty */
-			if (list_empty(&dummy_repoll))
-				list_add(&napi->poll_list, &dummy_repoll);
-
-			budget -= napi_poll(napi, &dummy_repoll);
-			if (unlikely(budget <= 0 ||
-				     time_after_eq(jiffies, time_limit))) {
-				cond_resched();
-
-				/* refresh the budget */
-				budget = netdev_budget;
-				__kfree_skb_flush();
-				time_limit = jiffies + 2;
-			}
+			local_bh_disable();
 
-			if (napi_disable_pending(napi))
-				again = false;
-			else if (!test_bit(NAPI_STATE_SCHED, &napi->state))
-				again = false;
-		} while (again);
+			have = netpoll_poll_lock(napi);
+			__napi_poll(napi, &repoll);
+			netpoll_poll_unlock(have);
 
-		__kfree_skb_flush();
-		local_bh_enable();
+			__kfree_skb_flush();
+			local_bh_enable();
+
+			if (!repoll)
+				break;
+
+			cond_resched();
+		}
 	}
 	return 0;
 }
-- 
2.28.0.618.gf4bc123cb7-goog