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![Thomas Gleixner](/assets/img/avatar_default.png)
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. Rename the reference count member to __rcuref to reflect the change. 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> Link: https://lore.kernel.org/r/20230307125538.989175656@linutronix.de Link: https://lore.kernel.org/r/20230323102800.215027837@linutronix.de Signed-off-by: Jakub Kicinski <kuba@kernel.org>
91 lines
2 KiB
C
91 lines
2 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/*
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* Handle firewalling core
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* Linux ethernet bridge
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*
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* Authors:
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* Lennert Buytenhek <buytenh@gnu.org>
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* Bart De Schuymer <bdschuym@pandora.be>
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*
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* Lennert dedicates this file to Kerstin Wurdinger.
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*/
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#include <linux/module.h>
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#include <linux/kernel.h>
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#include <linux/in_route.h>
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#include <linux/inetdevice.h>
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#include <net/route.h>
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#include "br_private.h"
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#ifdef CONFIG_SYSCTL
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#include <linux/sysctl.h>
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#endif
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static void fake_update_pmtu(struct dst_entry *dst, struct sock *sk,
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struct sk_buff *skb, u32 mtu,
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bool confirm_neigh)
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{
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}
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static void fake_redirect(struct dst_entry *dst, struct sock *sk,
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struct sk_buff *skb)
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{
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}
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static u32 *fake_cow_metrics(struct dst_entry *dst, unsigned long old)
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{
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return NULL;
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}
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static struct neighbour *fake_neigh_lookup(const struct dst_entry *dst,
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struct sk_buff *skb,
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const void *daddr)
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{
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return NULL;
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}
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static unsigned int fake_mtu(const struct dst_entry *dst)
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{
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return dst->dev->mtu;
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}
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static struct dst_ops fake_dst_ops = {
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.family = AF_INET,
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.update_pmtu = fake_update_pmtu,
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.redirect = fake_redirect,
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.cow_metrics = fake_cow_metrics,
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.neigh_lookup = fake_neigh_lookup,
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.mtu = fake_mtu,
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};
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/*
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* Initialize bogus route table used to keep netfilter happy.
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* Currently, we fill in the PMTU entry because netfilter
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* refragmentation needs it, and the rt_flags entry because
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* ipt_REJECT needs it. Future netfilter modules might
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* require us to fill additional fields.
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*/
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static const u32 br_dst_default_metrics[RTAX_MAX] = {
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[RTAX_MTU - 1] = 1500,
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};
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void br_netfilter_rtable_init(struct net_bridge *br)
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{
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struct rtable *rt = &br->fake_rtable;
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rcuref_init(&rt->dst.__rcuref, 1);
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rt->dst.dev = br->dev;
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dst_init_metrics(&rt->dst, br_dst_default_metrics, true);
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rt->dst.flags = DST_NOXFRM | DST_FAKE_RTABLE;
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rt->dst.ops = &fake_dst_ops;
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}
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int __init br_nf_core_init(void)
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{
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return dst_entries_init(&fake_dst_ops);
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}
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void br_nf_core_fini(void)
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{
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dst_entries_destroy(&fake_dst_ops);
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}
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