net: repack struct netdev_queue
Adding the NAPI pointer to struct netdev_queue made it grow into another cacheline, even though there was 44 bytes of padding available. The struct was historically grouped as follows: /* read-mostly stuff (align) */ /* ... random control path fields ... */ /* write-mostly stuff (align) */ /* ... 40 byte hole ... */ /* struct dql (align) */ It seems that people want to add control path fields after the read only fields. struct dql looks pretty innocent but it forces its own alignment and nothing indicates that there is a lot of empty space above it. Move dql above the xmit_lock. This shifts the empty space to the end of the struct rather than in the middle of it. Move two example fields there to set an example. Hopefully people will now add new fields at the end of the struct. A lot of the read-only stuff is also control path-only, but if we move it all we'll have another hole in the middle. Before: /* size: 384, cachelines: 6, members: 16 */ /* sum members: 284, holes: 3, sum holes: 100 */ After: /* size: 320, cachelines: 5, members: 16 */ /* sum members: 284, holes: 1, sum holes: 8 */ Reviewed-by: Eric Dumazet <edumazet@google.com> Link: https://patch.msgid.link/20240820205119.1321322-1-kuba@kernel.org Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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@ -644,9 +644,6 @@ struct netdev_queue {
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struct Qdisc __rcu *qdisc_sleeping;
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#ifdef CONFIG_SYSFS
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struct kobject kobj;
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#endif
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#if defined(CONFIG_XPS) && defined(CONFIG_NUMA)
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int numa_node;
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#endif
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unsigned long tx_maxrate;
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/*
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@ -660,13 +657,13 @@ struct netdev_queue {
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#ifdef CONFIG_XDP_SOCKETS
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struct xsk_buff_pool *pool;
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#endif
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/* NAPI instance for the queue
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* Readers and writers must hold RTNL
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*/
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struct napi_struct *napi;
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/*
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* write-mostly part
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*/
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#ifdef CONFIG_BQL
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struct dql dql;
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#endif
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spinlock_t _xmit_lock ____cacheline_aligned_in_smp;
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int xmit_lock_owner;
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/*
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@ -676,8 +673,16 @@ struct netdev_queue {
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unsigned long state;
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#ifdef CONFIG_BQL
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struct dql dql;
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/*
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* slow- / control-path part
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*/
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/* NAPI instance for the queue
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* Readers and writers must hold RTNL
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*/
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struct napi_struct *napi;
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#if defined(CONFIG_XPS) && defined(CONFIG_NUMA)
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int numa_node;
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#endif
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} ____cacheline_aligned_in_smp;
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