linux-kernel - [PATCH v2 net-next 2/2] net: introduce budget

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Date:   Tue, 14 Mar 2023 11:05:32 +0800
From:   Jason Xing <kerneljasonxing@...il.com>
To:     davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, ast@...nel.org, daniel@...earbox.net,
        hawk@...nel.org, john.fastabend@...il.com,
        stephen@...workplumber.org, simon.horman@...igine.com,
        sinquersw@...il.com
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, kerneljasonxing@...il.com,
        Jason Xing <kernelxing@...cent.com>
Subject: [PATCH v2 net-next 2/2] net: introduce budget_squeeze to help us tune rx behavior

From: Jason Xing <kernelxing@...cent.com>

When we encounter some performance issue and then get lost on how
to tune the budget limit and time limit in net_rx_action() function,
we can separately counting both of them to avoid the confusion.

Signed-off-by: Jason Xing <kernelxing@...cent.com>
---
v2:
1) change the coding style suggested by Stephen and Simon
2) Keep the display of the old data (time_squeeze) untouched suggested
by Kui-Feng
Link: https://lore.kernel.org/lkml/20230311163614.92296-1-kerneljasonxing@gmail.com/
---
 include/linux/netdevice.h |  1 +
 net/core/dev.c            | 12 ++++++++----
 net/core/net-procfs.c     |  9 ++++++---
 3 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 6a14b7b11766..5736311a2133 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3157,6 +3157,7 @@ struct softnet_data {
 	/* stats */
 	unsigned int		processed;
 	unsigned int		time_squeeze;
+	unsigned int		budget_squeeze;
 #ifdef CONFIG_RPS
 	struct softnet_data	*rps_ipi_list;
 #endif
diff --git a/net/core/dev.c b/net/core/dev.c
index 253584777101..1518a366783b 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6637,6 +6637,7 @@ static __latent_entropy void net_rx_action(struct softirq_action *h)
 	unsigned long time_limit = jiffies +
 		usecs_to_jiffies(READ_ONCE(netdev_budget_usecs));
 	int budget = READ_ONCE(netdev_budget);
+	bool done = false;
 	LIST_HEAD(list);
 	LIST_HEAD(repoll);
 
@@ -6644,7 +6645,7 @@ static __latent_entropy void net_rx_action(struct softirq_action *h)
 	list_splice_init(&sd->poll_list, &list);
 	local_irq_enable();
 
-	for (;;) {
+	while (!done) {
 		struct napi_struct *n;
 
 		skb_defer_free_flush(sd);
@@ -6662,10 +6663,13 @@ static __latent_entropy void net_rx_action(struct softirq_action *h)
 		 * Allow this to run for 2 jiffies since which will allow
 		 * an average latency of 1.5/HZ.
 		 */
-		if (unlikely(budget <= 0 ||
-			     time_after_eq(jiffies, time_limit))) {
+		if (unlikely(budget <= 0)) {
+			sd->budget_squeeze++;
+			done = true;
+		}
+		if (unlikely(time_after_eq(jiffies, time_limit))) {
 			sd->time_squeeze++;
-			break;
+			done = true;
 		}
 	}
 
diff --git a/net/core/net-procfs.c b/net/core/net-procfs.c
index 2809b663e78d..25810ee46a04 100644
--- a/net/core/net-procfs.c
+++ b/net/core/net-procfs.c
@@ -179,14 +179,17 @@ static int softnet_seq_show(struct seq_file *seq, void *v)
 	 */
 	seq_printf(seq,
 		   "%08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x "
-		   "%08x %08x\n",
-		   sd->processed, sd->dropped, sd->time_squeeze, 0,
+		   "%08x %08x %08x %08x\n",
+		   sd->processed, sd->dropped,
+		   sd->time_squeeze + sd->budget_squeeze, /* keep it untouched */
+		   0,
 		   0, 0, 0, 0, /* was fastroute */
 		   0,	/* was cpu_collision */
 		   sd->received_rps, flow_limit_count,
 		   softnet_backlog_len(sd),	/* keep it untouched */
 		   (int)seq->index,
-		   softnet_input_pkt_queue_len(sd), softnet_process_queue_len(sd));
+		   softnet_input_pkt_queue_len(sd), softnet_process_queue_len(sd),
+		   sd->time_squeeze, sd->budget_squeeze);
 	return 0;
 }
 
-- 
2.37.3