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@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/Documentation/sysctl/net.txt b/Documentation/sysctl/net.txt
index 2ebabc9..14db18c 100644 (file)
--- 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 0f3c38c..c49cf21 100644 (file)
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3296,6 +3296,7 @@ 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 e13d480..177f5f1 100644 (file)
--- 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 (file)
--- a/kernel/sysctl_binary.c
+++ b/kernel/sysctl_binary.c
@@ -197,6 +197,7 @@ static const struct bin_table bin_net_core_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 5d33e2b..1c53c05 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3441,6 +3441,7 @@ EXPORT_SYMBOL(netdev_max_backlog);
 
 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 */
@@ -5307,7 +5308,8 @@ out_unlock:
 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 (file)
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -452,6 +452,14 @@ static struct ctl_table net_core_table[] = {
                .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,
+       },
        { }
 };