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authorEric Dumazet <edumazet@google.com>2021-10-14 06:41:26 -0700
committerDavid S. Miller <davem@davemloft.net>2021-10-15 11:28:34 +0100
commit19757cebf0c5016a1f36f7fe9810a9f0b33c0832 (patch)
tree9d2349b63f328c9cb79fe6580215f823f8765b78 /net/dccp
parent0b93aed2842d950e8d2625e975e5a57febeff33d (diff)
downloadlinux-19757cebf0c5016a1f36f7fe9810a9f0b33c0832.tar.bz2
tcp: switch orphan_count to bare per-cpu counters
Use of percpu_counter structure to track count of orphaned sockets is causing problems on modern hosts with 256 cpus or more. Stefan Bach reported a serious spinlock contention in real workloads, that I was able to reproduce with a netfilter rule dropping incoming FIN packets. 53.56% server [kernel.kallsyms] [k] queued_spin_lock_slowpath | ---queued_spin_lock_slowpath | --53.51%--_raw_spin_lock_irqsave | --53.51%--__percpu_counter_sum tcp_check_oom | |--39.03%--__tcp_close | tcp_close | inet_release | inet6_release | sock_close | __fput | ____fput | task_work_run | exit_to_usermode_loop | do_syscall_64 | entry_SYSCALL_64_after_hwframe | __GI___libc_close | --14.48%--tcp_out_of_resources tcp_write_timeout tcp_retransmit_timer tcp_write_timer_handler tcp_write_timer call_timer_fn expire_timers __run_timers run_timer_softirq __softirqentry_text_start As explained in commit cf86a086a180 ("net/dst: use a smaller percpu_counter batch for dst entries accounting"), default batch size is too big for the default value of tcp_max_orphans (262144). But even if we reduce batch sizes, there would still be cases where the estimated count of orphans is beyond the limit, and where tcp_too_many_orphans() has to call the expensive percpu_counter_sum_positive(). One solution is to use plain per-cpu counters, and have a timer to periodically refresh this cache. Updating this cache every 100ms seems about right, tcp pressure state is not radically changing over shorter periods. percpu_counter was nice 15 years ago while hosts had less than 16 cpus, not anymore by current standards. v2: Fix the build issue for CONFIG_CRYPTO_DEV_CHELSIO_TLS=m, reported by kernel test robot <lkp@intel.com> Remove unused socket argument from tcp_too_many_orphans() Fixes: dd24c00191d5 ("net: Use a percpu_counter for orphan_count") Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: Stefan Bach <sfb@google.com> Cc: Neal Cardwell <ncardwell@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/dccp')
-rw-r--r--net/dccp/dccp.h2
-rw-r--r--net/dccp/proto.c14
2 files changed, 5 insertions, 11 deletions
diff --git a/net/dccp/dccp.h b/net/dccp/dccp.h
index c5c1d2b8045e..5183e627468d 100644
--- a/net/dccp/dccp.h
+++ b/net/dccp/dccp.h
@@ -48,7 +48,7 @@ extern bool dccp_debug;
extern struct inet_hashinfo dccp_hashinfo;
-extern struct percpu_counter dccp_orphan_count;
+DECLARE_PER_CPU(unsigned int, dccp_orphan_count);
void dccp_time_wait(struct sock *sk, int state, int timeo);
diff --git a/net/dccp/proto.c b/net/dccp/proto.c
index abb5c596a817..fc44dadc778b 100644
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -42,8 +42,8 @@ DEFINE_SNMP_STAT(struct dccp_mib, dccp_statistics) __read_mostly;
EXPORT_SYMBOL_GPL(dccp_statistics);
-struct percpu_counter dccp_orphan_count;
-EXPORT_SYMBOL_GPL(dccp_orphan_count);
+DEFINE_PER_CPU(unsigned int, dccp_orphan_count);
+EXPORT_PER_CPU_SYMBOL_GPL(dccp_orphan_count);
struct inet_hashinfo dccp_hashinfo;
EXPORT_SYMBOL_GPL(dccp_hashinfo);
@@ -1055,7 +1055,7 @@ adjudge_to_death:
bh_lock_sock(sk);
WARN_ON(sock_owned_by_user(sk));
- percpu_counter_inc(sk->sk_prot->orphan_count);
+ this_cpu_inc(dccp_orphan_count);
/* Have we already been destroyed by a softirq or backlog? */
if (state != DCCP_CLOSED && sk->sk_state == DCCP_CLOSED)
@@ -1115,13 +1115,10 @@ static int __init dccp_init(void)
BUILD_BUG_ON(sizeof(struct dccp_skb_cb) >
sizeof_field(struct sk_buff, cb));
- rc = percpu_counter_init(&dccp_orphan_count, 0, GFP_KERNEL);
- if (rc)
- goto out_fail;
inet_hashinfo_init(&dccp_hashinfo);
rc = inet_hashinfo2_init_mod(&dccp_hashinfo);
if (rc)
- goto out_free_percpu;
+ goto out_fail;
rc = -ENOBUFS;
dccp_hashinfo.bind_bucket_cachep =
kmem_cache_create("dccp_bind_bucket",
@@ -1226,8 +1223,6 @@ out_free_bind_bucket_cachep:
kmem_cache_destroy(dccp_hashinfo.bind_bucket_cachep);
out_free_hashinfo2:
inet_hashinfo2_free_mod(&dccp_hashinfo);
-out_free_percpu:
- percpu_counter_destroy(&dccp_orphan_count);
out_fail:
dccp_hashinfo.bhash = NULL;
dccp_hashinfo.ehash = NULL;
@@ -1250,7 +1245,6 @@ static void __exit dccp_fini(void)
dccp_ackvec_exit();
dccp_sysctl_exit();
inet_hashinfo2_free_mod(&dccp_hashinfo);
- percpu_counter_destroy(&dccp_orphan_count);
}
module_init(dccp_init);