Messages in this thread Patch in this message | | | From | Thomas Gleixner <> | Subject | [patch V2 4/4] net: dst: Switch to rcuref_t reference counting | Date | Tue, 7 Mar 2023 13:57:46 +0100 (CET) |
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Under high contention dst_entry::__refcnt becomes a significant bottleneck.
atomic_inc_not_zero() is implemented with a cmpxchg() loop, which goes into high retry rates on contention.
Switch the reference count to rcuref_t which results in a significant performance gain.
The gain depends on the micro-architecture and the number of concurrent operations and has been measured in the range of +25% to +130% with a localhost memtier/memcached benchmark which amplifies the problem massively.
Running the memtier/memcached benchmark over a real (1Gb) network connection the conversion on top of the false sharing fix for struct dst_entry::__refcnt results in a total gain in the 2%-5% range over the upstream baseline.
Reported-by: Wangyang Guo <wangyang.guo@intel.com> Reported-by: Arjan Van De Ven <arjan.van.de.ven@intel.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: "David S. Miller" <davem@davemloft.net> Cc: Eric Dumazet <edumazet@google.com> Cc: Jakub Kicinski <kuba@kernel.org> Cc: Paolo Abeni <pabeni@redhat.com> Cc: netdev@vger.kernel.org --- include/net/dst.h | 9 +++++---- include/net/sock.h | 2 +- net/bridge/br_nf_core.c | 2 +- net/core/dst.c | 26 +++++--------------------- net/core/rtnetlink.c | 2 +- net/ipv6/route.c | 6 +++--- net/netfilter/ipvs/ip_vs_xmit.c | 4 ++-- 7 files changed, 18 insertions(+), 33 deletions(-)
--- a/include/net/dst.h +++ b/include/net/dst.h @@ -16,6 +16,7 @@ #include <linux/bug.h> #include <linux/jiffies.h> #include <linux/refcount.h> +#include <linux/rcuref.h> #include <net/neighbour.h> #include <asm/processor.h> #include <linux/indirect_call_wrapper.h> @@ -65,7 +66,7 @@ struct dst_entry { * input/output/ops or performance tanks badly */ #ifdef CONFIG_64BIT - atomic_t __refcnt; /* 64-bit offset 64 */ + rcuref_t __refcnt; /* 64-bit offset 64 */ #endif int __use; unsigned long lastuse; @@ -75,7 +76,7 @@ struct dst_entry { __u32 tclassid; #ifndef CONFIG_64BIT struct lwtunnel_state *lwtstate; - atomic_t __refcnt; /* 32-bit offset 64 */ + rcuref_t __refcnt; /* 32-bit offset 64 */ #endif netdevice_tracker dev_tracker; @@ -241,7 +242,7 @@ static inline void dst_hold(struct dst_e * the placement of __refcnt in struct dst_entry */ BUILD_BUG_ON(offsetof(struct dst_entry, __refcnt) & 63); - WARN_ON(atomic_inc_not_zero(&dst->__refcnt) == 0); + WARN_ON(!rcuref_get(&dst->__refcnt)); } static inline void dst_use_noref(struct dst_entry *dst, unsigned long time) @@ -305,7 +306,7 @@ static inline void skb_dst_copy(struct s */ static inline bool dst_hold_safe(struct dst_entry *dst) { - return atomic_inc_not_zero(&dst->__refcnt); + return rcuref_get(&dst->__refcnt); } /** --- a/include/net/sock.h +++ b/include/net/sock.h @@ -2131,7 +2131,7 @@ sk_dst_get(struct sock *sk) rcu_read_lock(); dst = rcu_dereference(sk->sk_dst_cache); - if (dst && !atomic_inc_not_zero(&dst->__refcnt)) + if (dst && !rcuref_get(&dst->__refcnt)) dst = NULL; rcu_read_unlock(); return dst; --- a/net/bridge/br_nf_core.c +++ b/net/bridge/br_nf_core.c @@ -73,7 +73,7 @@ void br_netfilter_rtable_init(struct net { struct rtable *rt = &br->fake_rtable; - atomic_set(&rt->dst.__refcnt, 1); + rcuref_init(&rt->dst.__refcnt, 1); rt->dst.dev = br->dev; dst_init_metrics(&rt->dst, br_dst_default_metrics, true); rt->dst.flags = DST_NOXFRM | DST_FAKE_RTABLE; --- a/net/core/dst.c +++ b/net/core/dst.c @@ -66,7 +66,7 @@ void dst_init(struct dst_entry *dst, str dst->tclassid = 0; #endif dst->lwtstate = NULL; - atomic_set(&dst->__refcnt, initial_ref); + rcuref_init(&dst->__refcnt, initial_ref); dst->__use = 0; dst->lastuse = jiffies; dst->flags = flags; @@ -162,31 +162,15 @@ EXPORT_SYMBOL(dst_dev_put); void dst_release(struct dst_entry *dst) { - if (dst) { - int newrefcnt; - - newrefcnt = atomic_dec_return(&dst->__refcnt); - if (WARN_ONCE(newrefcnt < 0, "dst_release underflow")) - net_warn_ratelimited("%s: dst:%p refcnt:%d\n", - __func__, dst, newrefcnt); - if (!newrefcnt) - call_rcu_hurry(&dst->rcu_head, dst_destroy_rcu); - } + if (dst && rcuref_put(&dst->__refcnt)) + call_rcu_hurry(&dst->rcu_head, dst_destroy_rcu); } EXPORT_SYMBOL(dst_release); void dst_release_immediate(struct dst_entry *dst) { - if (dst) { - int newrefcnt; - - newrefcnt = atomic_dec_return(&dst->__refcnt); - if (WARN_ONCE(newrefcnt < 0, "dst_release_immediate underflow")) - net_warn_ratelimited("%s: dst:%p refcnt:%d\n", - __func__, dst, newrefcnt); - if (!newrefcnt) - dst_destroy(dst); - } + if (dst && rcuref_put(&dst->__refcnt)) + dst_destroy(dst); } EXPORT_SYMBOL(dst_release_immediate); --- a/net/core/rtnetlink.c +++ b/net/core/rtnetlink.c @@ -840,7 +840,7 @@ int rtnl_put_cacheinfo(struct sk_buff *s if (dst) { ci.rta_lastuse = jiffies_delta_to_clock_t(jiffies - dst->lastuse); ci.rta_used = dst->__use; - ci.rta_clntref = atomic_read(&dst->__refcnt); + ci.rta_clntref = rcuref_read(&dst->__refcnt); } if (expires) { unsigned long clock; --- a/net/ipv6/route.c +++ b/net/ipv6/route.c @@ -293,7 +293,7 @@ static const struct fib6_info fib6_null_ static const struct rt6_info ip6_null_entry_template = { .dst = { - .__refcnt = ATOMIC_INIT(1), + .__refcnt = RCUREF_INIT(1), .__use = 1, .obsolete = DST_OBSOLETE_FORCE_CHK, .error = -ENETUNREACH, @@ -307,7 +307,7 @@ static const struct rt6_info ip6_null_en static const struct rt6_info ip6_prohibit_entry_template = { .dst = { - .__refcnt = ATOMIC_INIT(1), + .__refcnt = RCUREF_INIT(1), .__use = 1, .obsolete = DST_OBSOLETE_FORCE_CHK, .error = -EACCES, @@ -319,7 +319,7 @@ static const struct rt6_info ip6_prohibi static const struct rt6_info ip6_blk_hole_entry_template = { .dst = { - .__refcnt = ATOMIC_INIT(1), + .__refcnt = RCUREF_INIT(1), .__use = 1, .obsolete = DST_OBSOLETE_FORCE_CHK, .error = -EINVAL, --- a/net/netfilter/ipvs/ip_vs_xmit.c +++ b/net/netfilter/ipvs/ip_vs_xmit.c @@ -339,7 +339,7 @@ static int spin_unlock_bh(&dest->dst_lock); IP_VS_DBG(10, "new dst %pI4, src %pI4, refcnt=%d\n", &dest->addr.ip, &dest_dst->dst_saddr.ip, - atomic_read(&rt->dst.__refcnt)); + rcuref_read(&rt->dst.__refcnt)); } if (ret_saddr) *ret_saddr = dest_dst->dst_saddr.ip; @@ -507,7 +507,7 @@ static int spin_unlock_bh(&dest->dst_lock); IP_VS_DBG(10, "new dst %pI6, src %pI6, refcnt=%d\n", &dest->addr.in6, &dest_dst->dst_saddr.in6, - atomic_read(&rt->dst.__refcnt)); + rcuref_read(&rt->dst.__refcnt)); } if (ret_saddr) *ret_saddr = dest_dst->dst_saddr.in6;
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