Re: [PATCH RT] net: move xmit_recursion to per-task variable on -RT

From: Sebastian Andrzej Siewior
Date: Thu Jan 14 2016 - 09:50:16 EST


* Thomas Gleixner | 2016-01-13 18:31:46 [+0100]:

>On Wed, 13 Jan 2016, Sebastian Andrzej Siewior wrote:
>> +#ifdef CONFIG_PREEMPT_RT_FULL
>> +static inline int dev_recursion_level(void)
>> +{
>> + return atomic_read(&current->xmit_recursion);
>
>Why would you need an atomic here. current does hardly race against itself.

right.

--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -2249,11 +2249,20 @@ void netdev_freemem(struct net_device *d
void synchronize_net(void);
int init_dummy_netdev(struct net_device *dev);

+#ifdef CONFIG_PREEMPT_RT_FULL
+static inline int dev_recursion_level(void)
+{
+ return current->xmit_recursion;
+}
+
+#else
+
DECLARE_PER_CPU(int, xmit_recursion);
static inline int dev_recursion_level(void)
{
return this_cpu_read(xmit_recursion);
}
+#endif

struct net_device *dev_get_by_index(struct net *net, int ifindex);
struct net_device *__dev_get_by_index(struct net *net, int ifindex);
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1851,6 +1851,9 @@ struct task_struct {
#ifdef CONFIG_DEBUG_ATOMIC_SLEEP
unsigned long task_state_change;
#endif
+#ifdef CONFIG_PREEMPT_RT_FULL
+ int xmit_recursion;
+#endif
int pagefault_disabled;
/* CPU-specific state of this task */
struct thread_struct thread;
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2940,9 +2940,44 @@ static void skb_update_prio(struct sk_bu
#define skb_update_prio(skb)
#endif

+#ifdef CONFIG_PREEMPT_RT_FULL
+
+static inline int xmit_rec_read(void)
+{
+ return current->xmit_recursion;
+}
+
+static inline void xmit_rec_inc(void)
+{
+ current->xmit_recursion++;
+}
+
+static inline void xmit_rec_dec(void)
+{
+ current->xmit_recursion--;
+}
+
+#else
+
DEFINE_PER_CPU(int, xmit_recursion);
EXPORT_SYMBOL(xmit_recursion);

+static inline int xmit_rec_read(void)
+{
+ return __this_cpu_read(xmit_recursion);
+}
+
+static inline void xmit_rec_inc(void)
+{
+ __this_cpu_inc(xmit_recursion);
+}
+
+static inline int xmit_rec_dec(void)
+{
+ __this_cpu_dec(xmit_recursion);
+}
+#endif
+
#define RECURSION_LIMIT 10

/**
@@ -3135,7 +3170,7 @@ static int __dev_queue_xmit(struct sk_bu

if (txq->xmit_lock_owner != cpu) {

- if (__this_cpu_read(xmit_recursion) > RECURSION_LIMIT)
+ if (xmit_rec_read() > RECURSION_LIMIT)
goto recursion_alert;

skb = validate_xmit_skb(skb, dev);
@@ -3145,9 +3180,9 @@ static int __dev_queue_xmit(struct sk_bu
HARD_TX_LOCK(dev, txq, cpu);

if (!netif_xmit_stopped(txq)) {
- __this_cpu_inc(xmit_recursion);
+ xmit_rec_inc();
skb = dev_hard_start_xmit(skb, dev, txq, &rc);
- __this_cpu_dec(xmit_recursion);
+ xmit_rec_dec();
if (dev_xmit_complete(rc)) {
HARD_TX_UNLOCK(dev, txq);
goto out;

>Thanks,
>
> tglx

Sebastian