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Replace 2 jiffies with sysctl netdev_budget_usecs to enable softirq tuning

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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>
This commit is contained in:
Matthew Whitehead 2017-04-19 12:37:10 -04:00 committed by David S. Miller
parent 20da848f8e
commit 7acf8a1e8a
6 changed files with 24 additions and 2 deletions
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11
Documentation/sysctl/net.txt
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@ -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
------------------

1
include/linux/netdevice.h
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@ -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);

1
include/uapi/linux/sysctl.h
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@ -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 */

1
kernel/sysctl_binary.c
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@ -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" },
{},
};

4
net/core/dev.c
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@ -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 @@ 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);

8
net/core/sysctl_net_core.c
View File

@ -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,
},
{ }
};