From 0b7d7f6b22084a3156f267c85303908a8f4c9a08 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 14 Jun 2019 16:22:20 -0700 Subject: [PATCH] tcp: add tcp_tx_skb_cache sysctl Feng Tang reported a performance regression after introduction of per TCP socket tx/rx caches, for TCP over loopback (netperf) There is high chance the regression is caused by a change on how well the 32 KB per-thread page (current->task_frag) can be recycled, and lack of pcp caches for order-3 pages. I could not reproduce the regression myself, cpus all being spinning on the mm spinlocks for page allocs/freeing, regardless of enabling or disabling the per tcp socket caches. It seems best to disable the feature by default, and let admins enabling it. MM layer either needs to provide scalable order-3 pages allocations, or could attempt a trylock on zone->lock if the caller only attempts to get a high-order page and is able to fallback to order-0 ones in case of pressure. Tests run on a 56 cores host (112 hyper threads) - 35.49% netperf [kernel.vmlinux] [k] queued_spin_lock_slowpath - 35.49% queued_spin_lock_slowpath - 18.18% get_page_from_freelist - __alloc_pages_nodemask - 18.18% alloc_pages_current skb_page_frag_refill sk_page_frag_refill tcp_sendmsg_locked tcp_sendmsg inet_sendmsg sock_sendmsg __sys_sendto __x64_sys_sendto do_syscall_64 entry_SYSCALL_64_after_hwframe __libc_send + 17.31% __free_pages_ok + 31.43% swapper [kernel.vmlinux] [k] intel_idle + 9.12% netperf [kernel.vmlinux] [k] copy_user_enhanced_fast_string + 6.53% netserver [kernel.vmlinux] [k] copy_user_enhanced_fast_string + 0.69% netserver [kernel.vmlinux] [k] queued_spin_lock_slowpath + 0.68% netperf [kernel.vmlinux] [k] skb_release_data + 0.52% netperf [kernel.vmlinux] [k] tcp_sendmsg_locked 0.46% netperf [kernel.vmlinux] [k] _raw_spin_lock_irqsave Fixes: 472c2e07eef0 ("tcp: add one skb cache for tx") Signed-off-by: Eric Dumazet Reported-by: Feng Tang Signed-off-by: David S. Miller --- include/net/sock.h | 4 +++- net/ipv4/sysctl_net_ipv4.c | 8 ++++++++ 2 files changed, 11 insertions(+), 1 deletion(-) diff --git a/include/net/sock.h b/include/net/sock.h index b02645e2dfad7..7d7f4ce63bb2a 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -1463,12 +1463,14 @@ static inline void sk_mem_uncharge(struct sock *sk, int size) __sk_mem_reclaim(sk, 1 << 20); } +DECLARE_STATIC_KEY_FALSE(tcp_tx_skb_cache_key); static inline void sk_wmem_free_skb(struct sock *sk, struct sk_buff *skb) { sock_set_flag(sk, SOCK_QUEUE_SHRUNK); sk->sk_wmem_queued -= skb->truesize; sk_mem_uncharge(sk, skb->truesize); - if (!sk->sk_tx_skb_cache && !skb_cloned(skb)) { + if (static_branch_unlikely(&tcp_tx_skb_cache_key) && + !sk->sk_tx_skb_cache && !skb_cloned(skb)) { skb_zcopy_clear(skb, true); sk->sk_tx_skb_cache = skb; return; diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c index 886b58d31351d..08a428a7b2749 100644 --- a/net/ipv4/sysctl_net_ipv4.c +++ b/net/ipv4/sysctl_net_ipv4.c @@ -54,6 +54,8 @@ static int one_day_secs = 24 * 3600; DEFINE_STATIC_KEY_FALSE(tcp_rx_skb_cache_key); EXPORT_SYMBOL(tcp_rx_skb_cache_key); +DEFINE_STATIC_KEY_FALSE(tcp_tx_skb_cache_key); + /* obsolete */ static int sysctl_tcp_low_latency __read_mostly; @@ -568,6 +570,12 @@ static struct ctl_table ipv4_table[] = { .mode = 0644, .proc_handler = proc_do_static_key, }, + { + .procname = "tcp_tx_skb_cache", + .data = &tcp_tx_skb_cache_key.key, + .mode = 0644, + .proc_handler = proc_do_static_key, + }, { } }; -- 2.39.2