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Date: Wed, 19 Apr 2017 12:37:10 -0400
From: Matthew Whitehead <tedheadster@...il.com>
To: netdev@...r.kernel.org
Cc: Matthew Whitehead <tedheadster@...il.com>
Subject: [PATCH net-next] Replace 2 jiffies with sysctl netdev_budget_usecs to enable softirq tuning
Constants used for tuning are generally a bad idea, especially as hardware
changes over time. Replace the constant 2 jiffies with sysctl variable
netdev_budget_usecs to enable sysadmins to tune the softirq processing.
Also document the variable.
For example, a very fast machine might tune this to 1000 microseconds,
while my regression testing 486DX-25 needs it to be 4000 microseconds on
a nearly idle network to prevent time_squeeze from being incremented.
Version 2: changed jiffies to microseconds for predictable units.
Signed-off-by: Matthew Whitehead <tedheadster@...il.com>
---
Documentation/sysctl/net.txt | 11 ++++++++++-
include/linux/netdevice.h | 1 +
include/uapi/linux/sysctl.h | 1 +
kernel/sysctl_binary.c | 1 +
net/core/dev.c | 4 +++-
net/core/sysctl_net_core.c | 8 ++++++++
6 files changed, 24 insertions(+), 2 deletions(-)
diff --git a/Documentation/sysctl/net.txt b/Documentation/sysctl/net.txt
index 2ebabc9..14db18c 100644
--- a/Documentation/sysctl/net.txt
+++ b/Documentation/sysctl/net.txt
@@ -188,7 +188,16 @@ netdev_budget
Maximum number of packets taken from all interfaces in one polling cycle (NAPI
poll). In one polling cycle interfaces which are registered to polling are
-probed in a round-robin manner.
+probed in a round-robin manner. Also, a polling cycle may not exceed
+netdev_budget_usecs microseconds, even if netdev_budget has not been
+exhausted.
+
+netdev_budget_usecs
+---------------------
+
+Maximum number of microseconds in one NAPI polling cycle. Polling
+will exit when either netdev_budget_usecs have elapsed during the
+poll cycle or the number of packets processed reaches netdev_budget.
netdev_max_backlog
------------------
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 97456b25..2fc72a5 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3305,6 +3305,7 @@ static __always_inline int ____dev_forward_skb(struct net_device *dev,
void dev_queue_xmit_nit(struct sk_buff *skb, struct net_device *dev);
extern int netdev_budget;
+extern unsigned int netdev_budget_usecs;
/* Called by rtnetlink.c:rtnl_unlock() */
void netdev_run_todo(void);
diff --git a/include/uapi/linux/sysctl.h b/include/uapi/linux/sysctl.h
index d2b1215..a1f1f25 100644
--- a/include/uapi/linux/sysctl.h
+++ b/include/uapi/linux/sysctl.h
@@ -274,6 +274,7 @@ enum
NET_CORE_AEVENT_ETIME=20,
NET_CORE_AEVENT_RSEQTH=21,
NET_CORE_WARNINGS=22,
+ NET_CORE_BUDGET_USECS=23,
};
/* /proc/sys/net/ethernet */
diff --git a/kernel/sysctl_binary.c b/kernel/sysctl_binary.c
index ece4b17..4ee3e49 100644
--- a/kernel/sysctl_binary.c
+++ b/kernel/sysctl_binary.c
@@ -197,6 +197,7 @@ struct bin_table {
{ CTL_INT, NET_CORE_AEVENT_ETIME, "xfrm_aevent_etime" },
{ CTL_INT, NET_CORE_AEVENT_RSEQTH, "xfrm_aevent_rseqth" },
{ CTL_INT, NET_CORE_WARNINGS, "warnings" },
+ { CTL_INT, NET_CORE_BUDGET_USECS, "netdev_budget_usecs" },
{},
};
diff --git a/net/core/dev.c b/net/core/dev.c
index 533a6d6..78627e5 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3441,6 +3441,7 @@ int dev_queue_xmit_accel(struct sk_buff *skb, void *accel_priv)
int netdev_tstamp_prequeue __read_mostly = 1;
int netdev_budget __read_mostly = 300;
+unsigned int __read_mostly netdev_budget_usecs = 2000;
int weight_p __read_mostly = 64; /* old backlog weight */
int dev_weight_rx_bias __read_mostly = 1; /* bias for backlog weight */
int dev_weight_tx_bias __read_mostly = 1; /* bias for output_queue quota */
@@ -5310,7 +5311,8 @@ static int napi_poll(struct napi_struct *n, struct list_head *repoll)
static __latent_entropy void net_rx_action(struct softirq_action *h)
{
struct softnet_data *sd = this_cpu_ptr(&softnet_data);
- unsigned long time_limit = jiffies + 2;
+ unsigned long time_limit = jiffies +
+ usecs_to_jiffies(netdev_budget_usecs);
int budget = netdev_budget;
LIST_HEAD(list);
LIST_HEAD(repoll);
diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index 7f9cc40..ea23254 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -452,6 +452,14 @@ static int proc_do_rss_key(struct ctl_table *table, int write,
.extra1 = &one,
.extra2 = &max_skb_frags,
},
+ {
+ .procname = "netdev_budget_usecs",
+ .data = &netdev_budget_usecs,
+ .maxlen = sizeof(unsigned int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &zero,
+ },
{ }
};
--
1.8.3.1
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