net: dev_weight: TX/RX orthogonality

Oftenly, introducing side effects on packet processing on the other half
of the stack by adjusting one of TX/RX via sysctl is not desirable.
There are cases of demand for asymmetric, orthogonal configurability.

This holds true especially for nodes where RPS for RFS usage on top is
configured and therefore use the 'old dev_weight'. This is quite a
common base configuration setup nowadays, even with NICs of superior processing
support (e.g. aRFS).

A good example use case are nodes acting as noSQL data bases with a
large number of tiny requests and rather fewer but large packets as responses.
It's affordable to have large budget and rx dev_weights for the
requests. But as a side effect having this large a number on TX
processed in one run can overwhelm drivers.

This patch therefore introduces an independent configurability via sysctl to
userland.

Signed-off-by: Matthias Tafelmeier <matthias.tafelmeier@gmx.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/Documentation/sysctl/net.txt b/Documentation/sysctl/net.txt
index f0480f7ea7404c777c1a8943047278d6765a4fe6..b80fbd4e557596beec9dc7acb30776d33ff673e7 100644 (file)
--- a/Documentation/sysctl/net.txt
+++ b/Documentation/sysctl/net.txt
@@ -61,6 +61,27 @@ The maximum number of packets that kernel can handle on a NAPI interrupt,
 it's a Per-CPU variable.
 Default: 64
 
+dev_weight_rx_bias
+--------------
+
+RPS (e.g. RFS, aRFS) processing is competing with the registered NAPI poll function
+of the driver for the per softirq cycle netdev_budget. This parameter influences
+the proportion of the configured netdev_budget that is spent on RPS based packet
+processing during RX softirq cycles. It is further meant for making current
+dev_weight adaptable for asymmetric CPU needs on RX/TX side of the network stack.
+(see dev_weight_tx_bias) It is effective on a per CPU basis. Determination is based
+on dev_weight and is calculated multiplicative (dev_weight * dev_weight_rx_bias).
+Default: 1
+
+dev_weight_tx_bias
+--------------
+
+Scales the maximum number of packets that can be processed during a TX softirq cycle.
+Effective on a per CPU basis. Allows scaling of current dev_weight for asymmetric
+net stack processing needs. Be careful to avoid making TX softirq processing a CPU hog.
+Calculation is based on dev_weight (dev_weight * dev_weight_tx_bias).
+Default: 1
+
 default_qdisc
 --------------
 

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 994f7423a74bd622884c3b646f4123d28697b8ad..ecd78b3c9abad01e14eeae97678c0060a13c6edb 100644 (file)
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3795,6 +3795,10 @@ void netdev_stats_to_stats64(struct rtnl_link_stats64 *stats64,
 extern int             netdev_max_backlog;
 extern int             netdev_tstamp_prequeue;
 extern int             weight_p;
+extern int             dev_weight_rx_bias;
+extern int             dev_weight_tx_bias;
+extern int             dev_rx_weight;
+extern int             dev_tx_weight;
 
 bool netdev_has_upper_dev(struct net_device *dev, struct net_device *upper_dev);
 struct net_device *netdev_upper_get_next_dev_rcu(struct net_device *dev,

diff --git a/net/core/dev.c b/net/core/dev.c
index 8db5a0b4b52061afe9cd44dead33cc69523d15df..56818f7eab2be7f2e5c632b135f2e4e49f7e2c63 100644 (file)
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -3427,7 +3427,11 @@ EXPORT_SYMBOL(netdev_max_backlog);
 
 int netdev_tstamp_prequeue __read_mostly = 1;
 int netdev_budget __read_mostly = 300;
-int weight_p __read_mostly = 64;            /* old backlog weight */
+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 */
+int dev_rx_weight __read_mostly = 64;
+int dev_tx_weight __read_mostly = 64;
 
 /* Called with irq disabled */
 static inline void ____napi_schedule(struct softnet_data *sd,
@@ -4833,7 +4837,7 @@ static int process_backlog(struct napi_struct *napi, int quota)
                net_rps_action_and_irq_enable(sd);
        }
 
-       napi->weight = weight_p;
+       napi->weight = dev_rx_weight;
        while (again) {
                struct sk_buff *skb;
 

diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index 2a46e4009f62d8c2ac8949789ae9626b0c016a11..eaa72eb0399c04dfbae61e22033802a31a8b90a4 100644 (file)
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -222,6 +222,21 @@ static int set_default_qdisc(struct ctl_table *table, int write,
 }
 #endif
 
+static int proc_do_dev_weight(struct ctl_table *table, int write,
+                          void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+       int ret;
+
+       ret = proc_dointvec(table, write, buffer, lenp, ppos);
+       if (ret != 0)
+               return ret;
+
+       dev_rx_weight = weight_p * dev_weight_rx_bias;
+       dev_tx_weight = weight_p * dev_weight_tx_bias;
+
+       return ret;
+}
+
 static int proc_do_rss_key(struct ctl_table *table, int write,
                           void __user *buffer, size_t *lenp, loff_t *ppos)
 {
@@ -273,7 +288,21 @@ static struct ctl_table net_core_table[] = {
                .data           = &weight_p,
                .maxlen         = sizeof(int),
                .mode           = 0644,
-               .proc_handler   = proc_dointvec
+               .proc_handler   = proc_do_dev_weight,
+       },
+       {
+               .procname       = "dev_weight_rx_bias",
+               .data           = &dev_weight_rx_bias,
+               .maxlen         = sizeof(int),
+               .mode           = 0644,
+               .proc_handler   = proc_do_dev_weight,
+       },
+       {
+               .procname       = "dev_weight_tx_bias",
+               .data           = &dev_weight_tx_bias,
+               .maxlen         = sizeof(int),
+               .mode           = 0644,
+               .proc_handler   = proc_do_dev_weight,
        },
        {
                .procname       = "netdev_max_backlog",

diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 6eb9c8e88519a36fc3ef82be7c7f1dbe0ef1e13c..b052b27a984e39c244c94132f1162a7033e5cc63 100644 (file)
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -247,7 +247,7 @@ static inline int qdisc_restart(struct Qdisc *q, int *packets)
 
 void __qdisc_run(struct Qdisc *q)
 {
-       int quota = weight_p;
+       int quota = dev_tx_weight;
        int packets;
 
        while (qdisc_restart(q, &packets)) {