From 6510ea973d8d9d4a0cb2fb557b36bd1ab3eb49f6 Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Mon, 25 Apr 2022 18:39:46 +0200 Subject: net: Use this_cpu_inc() to increment net->core_stats The macro dev_core_stats_##FIELD##_inc() disables preemption and invokes netdev_core_stats_alloc() to return a per-CPU pointer. netdev_core_stats_alloc() will allocate memory on its first invocation which breaks on PREEMPT_RT because it requires non-atomic context for memory allocation. This can be avoided by enabling preemption in netdev_core_stats_alloc() assuming the caller always disables preemption. It might be better to replace local_inc() with this_cpu_inc() now that dev_core_stats_##FIELD##_inc() gained a preempt-disable section and does not rely on already disabled preemption. This results in less instructions on x86-64: local_inc: | incl %gs:__preempt_count(%rip) # __preempt_count | movq 488(%rdi), %rax # _1->core_stats, _22 | testq %rax, %rax # _22 | je .L585 #, | add %gs:this_cpu_off(%rip), %rax # this_cpu_off, tcp_ptr__ | .L586: | testq %rax, %rax # _27 | je .L587 #, | incq (%rax) # _6->a.counter | .L587: | decl %gs:__preempt_count(%rip) # __preempt_count this_cpu_inc(), this patch: | movq 488(%rdi), %rax # _1->core_stats, _5 | testq %rax, %rax # _5 | je .L591 #, | .L585: | incq %gs:(%rax) # _18->rx_dropped Use unsigned long as type for the counter. Use this_cpu_inc() to increment the counter. Use a plain read of the counter. Signed-off-by: Sebastian Andrzej Siewior Reviewed-by: Eric Dumazet Link: https://lore.kernel.org/r/YmbO0pxgtKpCw4SY@linutronix.de Signed-off-by: Jakub Kicinski --- include/linux/netdevice.h | 21 +++++++++------------ 1 file changed, 9 insertions(+), 12 deletions(-) (limited to 'include/linux') diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h index 59e27a2b7bf0..b1fbe21650bb 100644 --- a/include/linux/netdevice.h +++ b/include/linux/netdevice.h @@ -199,10 +199,10 @@ struct net_device_stats { * Try to fit them in a single cache line, for dev_get_stats() sake. */ struct net_device_core_stats { - local_t rx_dropped; - local_t tx_dropped; - local_t rx_nohandler; -} __aligned(4 * sizeof(local_t)); + unsigned long rx_dropped; + unsigned long tx_dropped; + unsigned long rx_nohandler; +} __aligned(4 * sizeof(unsigned long)); #include #include @@ -3843,15 +3843,15 @@ static __always_inline bool __is_skb_forwardable(const struct net_device *dev, return false; } -struct net_device_core_stats *netdev_core_stats_alloc(struct net_device *dev); +struct net_device_core_stats __percpu *netdev_core_stats_alloc(struct net_device *dev); -static inline struct net_device_core_stats *dev_core_stats(struct net_device *dev) +static inline struct net_device_core_stats __percpu *dev_core_stats(struct net_device *dev) { /* This READ_ONCE() pairs with the write in netdev_core_stats_alloc() */ struct net_device_core_stats __percpu *p = READ_ONCE(dev->core_stats); if (likely(p)) - return this_cpu_ptr(p); + return p; return netdev_core_stats_alloc(dev); } @@ -3859,14 +3859,11 @@ static inline struct net_device_core_stats *dev_core_stats(struct net_device *de #define DEV_CORE_STATS_INC(FIELD) \ static inline void dev_core_stats_##FIELD##_inc(struct net_device *dev) \ { \ - struct net_device_core_stats *p; \ + struct net_device_core_stats __percpu *p; \ \ - preempt_disable(); \ p = dev_core_stats(dev); \ - \ if (p) \ - local_inc(&p->FIELD); \ - preempt_enable(); \ + this_cpu_inc(p->FIELD); \ } DEV_CORE_STATS_INC(rx_dropped) DEV_CORE_STATS_INC(tx_dropped) -- cgit