[linux-next,v2] net: record times of netdev_budget exhausted
Commit Message
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(-)
Comments
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.
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.
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.
@@ -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
@@ -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;
}
@@ -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;
}