[PATCH linux-next v2] net: record times of netdev_budget exhausted

yang.yang29@zte.com.cn posted 1 patch 1 year, 3 months ago
include/linux/netdevice.h |  1 +
net/core/dev.c            | 11 +++++++----
net/core/net-procfs.c     |  5 +++--
3 files changed, 11 insertions(+), 6 deletions(-)
[PATCH linux-next v2] net: record times of netdev_budget exhausted
Posted by yang.yang29@zte.com.cn 1 year, 3 months ago
From: Yang Yang <yang.yang29@zte.com>

A long time ago time_squeeze was used to only record netdev_budget
exhausted[1]. Then we added netdev_budget_usecs to enable softirq
tuning[2]. And when polling elapsed netdev_budget_usecs, it's also
record by time_squeeze.
For tuning netdev_budget and netdev_budget_usecs respectively, we'd
better distinguish from netdev_budget exhausted and netdev_budget_usecs
elapsed, so add budget_exhaust to record netdev_budget exhausted.

[1] commit 1da177e4c3f4("Linux-2.6.12-rc2")
[2] commit 7acf8a1e8a28("Replace 2 jiffies with sysctl netdev_budget_usecs to enable softirq tuning")

Signed-off-by: Yang Yang <yang.yang29@zte.com>
Reviewed-by: xu xin <xu.xin16@zte.com.cn>
Reviewed-by: Zhang Yunkai <zhang.yunkai@zte.com.cn>
---
Changes since v1: - Fix compile error of patch making error
---
 include/linux/netdevice.h |  1 +
 net/core/dev.c            | 11 +++++++----
 net/core/net-procfs.c     |  5 +++--
 3 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 5aa35c58c342..a77719b956a6 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3135,6 +3135,7 @@ struct softnet_data {
 	/* stats */
 	unsigned int		processed;
 	unsigned int		time_squeeze;
+	unsigned int		budget_exhaust;
 #ifdef CONFIG_RPS
 	struct softnet_data	*rps_ipi_list;
 #endif
diff --git a/net/core/dev.c b/net/core/dev.c
index 7627c475d991..42ae2dc62661 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6663,11 +6663,14 @@ static __latent_entropy void net_rx_action(struct softirq_action *h)
 		budget -= napi_poll(n, &repoll);

 		/* If softirq window is exhausted then punt.
-		 * Allow this to run for 2 jiffies since which will allow
-		 * an average latency of 1.5/HZ.
+		 * The window is controlled by packets budget and time.
+		 * See Documentation/admin-guide/sysctl/net.rst for details.
 		 */
-		if (unlikely(budget <= 0 ||
-			     time_after_eq(jiffies, time_limit))) {
+		if (unlikely(budget <= 0)) {
+			sd->budget_exhaust++;
+			break;
+		}
+		if (unlikely(time_after_eq(jiffies, time_limit))) {
 			sd->time_squeeze++;
 			break;
 		}
diff --git a/net/core/net-procfs.c b/net/core/net-procfs.c
index 1ec23bf8b05c..e09e245125f0 100644
--- a/net/core/net-procfs.c
+++ b/net/core/net-procfs.c
@@ -169,12 +169,13 @@ static int softnet_seq_show(struct seq_file *seq, void *v)
 	 * mapping the data a specific CPU
 	 */
 	seq_printf(seq,
-		   "%08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x\n",
+		   "%08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x %08x\n",
 		   sd->processed, sd->dropped, sd->time_squeeze, 0,
 		   0, 0, 0, 0, /* was fastroute */
 		   0,	/* was cpu_collision */
 		   sd->received_rps, flow_limit_count,
-		   softnet_backlog_len(sd), (int)seq->index);
+		   softnet_backlog_len(sd), (int)seq->index,
+		   sd->budget_exhaust);
 	return 0;
 }

-- 
2.15.2
Re: [PATCH linux-next v2] net: record times of netdev_budget exhausted
Posted by Jakub Kicinski 1 year, 3 months ago
On Mon, 5 Dec 2022 09:36:12 +0800 (CST) yang.yang29@zte.com.cn wrote:
> A long time ago time_squeeze was used to only record netdev_budget
> exhausted[1]. Then we added netdev_budget_usecs to enable softirq
> tuning[2]. And when polling elapsed netdev_budget_usecs, it's also
> record by time_squeeze.
> For tuning netdev_budget and netdev_budget_usecs respectively, we'd
> better distinguish from netdev_budget exhausted and netdev_budget_usecs
> elapsed, so add budget_exhaust to record netdev_budget exhausted.
> 
> [1] commit 1da177e4c3f4("Linux-2.6.12-rc2")
> [2] commit 7acf8a1e8a28("Replace 2 jiffies with sysctl netdev_budget_usecs to enable softirq tuning")

Same comments as on v1.
Re: [PATCH linux-next v2] net: record times of netdev_budget exhausted
Posted by Eric Dumazet 1 year, 3 months ago
On Tue, Dec 6, 2022 at 2:53 AM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Mon, 5 Dec 2022 09:36:12 +0800 (CST) yang.yang29@zte.com.cn wrote:
> > A long time ago time_squeeze was used to only record netdev_budget
> > exhausted[1]. Then we added netdev_budget_usecs to enable softirq
> > tuning[2]. And when polling elapsed netdev_budget_usecs, it's also
> > record by time_squeeze.
> > For tuning netdev_budget and netdev_budget_usecs respectively, we'd
> > better distinguish from netdev_budget exhausted and netdev_budget_usecs
> > elapsed, so add budget_exhaust to record netdev_budget exhausted.
> >
> > [1] commit 1da177e4c3f4("Linux-2.6.12-rc2")
> > [2] commit 7acf8a1e8a28("Replace 2 jiffies with sysctl netdev_budget_usecs to enable softirq tuning")
>
> Same comments as on v1.

Yes, and if we really want to track all these kinds of events the
break caused by need_resched() in do_softirq would
also need some monitoring.

I feel that more granular tracing (did I say tracepoints) would be more useful.
Re: [PATCH linux-next v2] net: record times of netdev_budget exhausted
Posted by yang.yang29@zte.com.cn 1 year, 3 months ago
On Tue, Dec 6, 2022 at 11:18 AM Eric Dumazet <edumazet@google.com,> wrote:
> Yes, and if we really want to track all these kinds of events the
> break caused by need_resched() in do_softirq would
> also need some monitoring.

I think this situation is a bit different. The break caused by
need_resched() in __do_softirq() is some kind of internal
events, kernel hacker may track it by something like tracepoint.

But netdev_budget* are sysctl for administrator, when
administrator adjust them, they may want to see the
effect in a direct or easy way.