net: reorganize sk_buff for faster __copy_skb_header()

With proliferation of bit fields in sk_buff, __copy_skb_header() became
quite expensive, showing as the most expensive function in a GSO
workload.

__copy_skb_header() performance is also critical for non GSO TCP
operations, as it is used from skb_clone()

This patch carefully moves all the fields that were not copied in a
separate zone : cloned, nohdr, fclone, peeked, head_frag, xmit_more

Then I moved all other fields and all other copied fields in a section
delimited by headers_start[0]/headers_end[0] section so that we
can use a single memcpy() call, inlined by compiler using long
word load/stores.

I also tried to make all copies in the natural orders of sk_buff,
to help hardware prefetching.

I made sure sk_buff size did not change.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 113 insertions, 100 deletions

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 8eaa62400fca..b6cced304b26 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -527,27 +527,41 @@ struct sk_buff {
         char                    cb[48] __aligned(8);
 
         unsigned long           _skb_refdst;
+        void                    (*destructor)(struct sk_buff *skb);
 #ifdef CONFIG_XFRM
         struct  sec_path        *sp;
 #endif
+#if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
+        struct nf_conntrack     *nfct;
+#endif
+#ifdef CONFIG_BRIDGE_NETFILTER
+        struct nf_bridge_info   *nf_bridge;
+#endif
         unsigned int            len,
                                 data_len;
         __u16                   mac_len,
                                 hdr_len;
-        union {
-                __wsum          csum;
-                struct {
-                        __u16   csum_start;
-                        __u16   csum_offset;
-                };
-        };
-        __u32                   priority;
+
+        /* Following fields are _not_ copied in __copy_skb_header()
+         * Note that queue_mapping is here mostly to fill a hole.
+         */
         kmemcheck_bitfield_begin(flags1);
-        __u8                    ignore_df:1,
-                                cloned:1,
-                                ip_summed:2,
+        __u16                   queue_mapping;
+        __u8                    cloned:1,
                                 nohdr:1,
-                                nfctinfo:3;
+                                fclone:2,
+                                peeked:1,
+                                head_frag:1,
+                                xmit_more:1;
+        /* one bit hole */
+        kmemcheck_bitfield_end(flags1);
+
+
+
+        /* fields enclosed in headers_start/headers_end are copied
+         * using a single memcpy() in __copy_skb_header()
+         */
+        __u32                   headers_start[0];
 
 /* if you move pkt_type around you also must adapt those constants */
 #ifdef __BIG_ENDIAN_BITFIELD
@@ -558,58 +572,53 @@ struct sk_buff {
 #define PKT_TYPE_OFFSET()       offsetof(struct sk_buff, __pkt_type_offset)
 
         __u8                    __pkt_type_offset[0];
-        __u8                    pkt_type:3,
-                                fclone:2,
-                                ipvs_property:1,
-                                peeked:1,
-                                nf_trace:1;
-        kmemcheck_bitfield_end(flags1);
-        __be16                  protocol;
-
-        void                    (*destructor)(struct sk_buff *skb);
-#if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
-        struct nf_conntrack     *nfct;
-#endif
-#ifdef CONFIG_BRIDGE_NETFILTER
-        struct nf_bridge_info   *nf_bridge;
-#endif
-
-        int                     skb_iif;
-
-        __u32                   hash;
-
-        __be16                  vlan_proto;
-        __u16                   vlan_tci;
-
-#ifdef CONFIG_NET_SCHED
-        __u16                   tc_index;       /* traffic control index */
-#ifdef CONFIG_NET_CLS_ACT
-        __u16                   tc_verd;        /* traffic control verdict */
-#endif
-#endif
-
-        __u16                   queue_mapping;
-        kmemcheck_bitfield_begin(flags2);
-        __u8                    xmit_more:1;
-#ifdef CONFIG_IPV6_NDISC_NODETYPE
-        __u8                    ndisc_nodetype:2;
-#endif
+        __u8                    pkt_type:3;
         __u8                    pfmemalloc:1;
+        __u8                    ignore_df:1;
+        __u8                    nfctinfo:3;
+
+        __u8                    nf_trace:1;
+        __u8                    ip_summed:2;
         __u8                    ooo_okay:1;
         __u8                    l4_hash:1;
         __u8                    sw_hash:1;
         __u8                    wifi_acked_valid:1;
         __u8                    wifi_acked:1;
+
         __u8                    no_fcs:1;
-        __u8                    head_frag:1;
         /* Indicates the inner headers are valid in the skbuff. */
         __u8                    encapsulation:1;
         __u8                    encap_hdr_csum:1;
         __u8                    csum_valid:1;
         __u8                    csum_complete_sw:1;
-        /* 1/3 bit hole (depending on ndisc_nodetype presence) */
-        kmemcheck_bitfield_end(flags2);
+        __u8                    csum_level:2;
+        __u8                    csum_bad:1;
 
+#ifdef CONFIG_IPV6_NDISC_NODETYPE
+        __u8                    ndisc_nodetype:2;
+#endif
+        __u8                    ipvs_property:1;
+        /* 5 or 7 bit hole */
+
+#ifdef CONFIG_NET_SCHED
+        __u16                   tc_index;       /* traffic control index */
+#ifdef CONFIG_NET_CLS_ACT
+        __u16                   tc_verd;        /* traffic control verdict */
+#endif
+#endif
+
+        union {
+                __wsum          csum;
+                struct {
+                        __u16   csum_start;
+                        __u16   csum_offset;
+                };
+        };
+        __u32                   priority;
+        int                     skb_iif;
+        __u32                   hash;
+        __be16                  vlan_proto;
+        __u16                   vlan_tci;
 #if defined CONFIG_NET_DMA || defined CONFIG_NET_RX_BUSY_POLL
         union {
                 unsigned int    napi_id;
@@ -625,19 +634,18 @@ struct sk_buff {
                 __u32           reserved_tailroom;
         };
 
-        kmemcheck_bitfield_begin(flags3);
-        __u8                    csum_level:2;
-        __u8                    csum_bad:1;
-        /* 13 bit hole */
-        kmemcheck_bitfield_end(flags3);
-
         __be16                  inner_protocol;
         __u16                   inner_transport_header;
         __u16                   inner_network_header;
         __u16                   inner_mac_header;
+
+        __be16                  protocol;
         __u16                   transport_header;
         __u16                   network_header;
         __u16                   mac_header;
+
+        __u32                   headers_end[0];
+
         /* These elements must be at the end, see alloc_skb() for details.  */
         sk_buff_data_t          tail;
         sk_buff_data_t          end;
@@ -3040,19 +3048,22 @@ static inline void nf_reset_trace(struct sk_buff *skb)
 }
 
 /* Note: This doesn't put any conntrack and bridge info in dst. */
-static inline void __nf_copy(struct sk_buff *dst, const struct sk_buff *src)
+static inline void __nf_copy(struct sk_buff *dst, const struct sk_buff *src,
+                             bool copy)
 {
 #if defined(CONFIG_NF_CONNTRACK) || defined(CONFIG_NF_CONNTRACK_MODULE)
         dst->nfct = src->nfct;
         nf_conntrack_get(src->nfct);
-        dst->nfctinfo = src->nfctinfo;
+        if (copy)
+                dst->nfctinfo = src->nfctinfo;
 #endif
 #ifdef CONFIG_BRIDGE_NETFILTER
         dst->nf_bridge  = src->nf_bridge;
         nf_bridge_get(src->nf_bridge);
 #endif
 #if IS_ENABLED(CONFIG_NETFILTER_XT_TARGET_TRACE) || defined(CONFIG_NF_TABLES)
-        dst->nf_trace = src->nf_trace;
+        if (copy)
+                dst->nf_trace = src->nf_trace;
 #endif
 }
 
@@ -3064,7 +3075,7 @@ static inline void nf_copy(struct sk_buff *dst, const struct sk_buff *src)
 #ifdef CONFIG_BRIDGE_NETFILTER
         nf_bridge_put(dst->nf_bridge);
 #endif
-        __nf_copy(dst, src);
+        __nf_copy(dst, src, true);
 }
 
 #ifdef CONFIG_NETWORK_SECMARK
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index d4fdc649112c..4be570a4ab21 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -261,7 +261,6 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
                 atomic_t *fclone_ref = (atomic_t *) (child + 1);
 
                 kmemcheck_annotate_bitfield(child, flags1);
-                kmemcheck_annotate_bitfield(child, flags2);
                 skb->fclone = SKB_FCLONE_ORIG;
                 atomic_set(fclone_ref, 1);
 
@@ -675,57 +674,61 @@ void consume_skb(struct sk_buff *skb)
 }
 EXPORT_SYMBOL(consume_skb);
 
+/* Make sure a field is enclosed inside headers_start/headers_end section */
+#define CHECK_SKB_FIELD(field) \
+        BUILD_BUG_ON(offsetof(struct sk_buff, field) <          \
+                     offsetof(struct sk_buff, headers_start));  \
+        BUILD_BUG_ON(offsetof(struct sk_buff, field) >          \
+                     offsetof(struct sk_buff, headers_end));    \
+
 static void __copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
 {
         new->tstamp             = old->tstamp;
+        /* We do not copy old->sk */
         new->dev                = old->dev;
-        new->transport_header   = old->transport_header;
-        new->network_header     = old->network_header;
-        new->mac_header         = old->mac_header;
-        new->inner_protocol     = old->inner_protocol;
-        new->inner_transport_header = old->inner_transport_header;
-        new->inner_network_header = old->inner_network_header;
-        new->inner_mac_header = old->inner_mac_header;
+        memcpy(new->cb, old->cb, sizeof(old->cb));
         skb_dst_copy(new, old);
-        skb_copy_hash(new, old);
-        new->ooo_okay           = old->ooo_okay;
-        new->no_fcs             = old->no_fcs;
-        new->encapsulation      = old->encapsulation;
-        new->encap_hdr_csum     = old->encap_hdr_csum;
-        new->csum_valid         = old->csum_valid;
-        new->csum_complete_sw   = old->csum_complete_sw;
 #ifdef CONFIG_XFRM
         new->sp                 = secpath_get(old->sp);
 #endif
-        memcpy(new->cb, old->cb, sizeof(old->cb));
-        new->csum               = old->csum;
-        new->ignore_df          = old->ignore_df;
-        new->pkt_type           = old->pkt_type;
-        new->ip_summed          = old->ip_summed;
-        skb_copy_queue_mapping(new, old);
-        new->priority           = old->priority;
-#if IS_ENABLED(CONFIG_IP_VS)
-        new->ipvs_property      = old->ipvs_property;
+        __nf_copy(new, old, false);
+
+        /* Note : this field could be in headers_start/headers_end section
+         * It is not yet because we do not want to have a 16 bit hole
+         */
+        new->queue_mapping = old->queue_mapping;
+
+        memcpy(&new->headers_start, &old->headers_start,
+               offsetof(struct sk_buff, headers_end) -
+               offsetof(struct sk_buff, headers_start));
+        CHECK_SKB_FIELD(protocol);
+        CHECK_SKB_FIELD(csum);
+        CHECK_SKB_FIELD(hash);
+        CHECK_SKB_FIELD(priority);
+        CHECK_SKB_FIELD(skb_iif);
+        CHECK_SKB_FIELD(vlan_proto);
+        CHECK_SKB_FIELD(vlan_tci);
+        CHECK_SKB_FIELD(transport_header);
+        CHECK_SKB_FIELD(network_header);
+        CHECK_SKB_FIELD(mac_header);
+        CHECK_SKB_FIELD(inner_protocol);
+        CHECK_SKB_FIELD(inner_transport_header);
+        CHECK_SKB_FIELD(inner_network_header);
+        CHECK_SKB_FIELD(inner_mac_header);
+        CHECK_SKB_FIELD(mark);
+#ifdef CONFIG_NETWORK_SECMARK
+        CHECK_SKB_FIELD(secmark);
+#endif
+#ifdef CONFIG_NET_RX_BUSY_POLL
+        CHECK_SKB_FIELD(napi_id);
 #endif
-        new->pfmemalloc         = old->pfmemalloc;
-        new->protocol           = old->protocol;
-        new->mark               = old->mark;
-        new->skb_iif            = old->skb_iif;
-        __nf_copy(new, old);
 #ifdef CONFIG_NET_SCHED
-        new->tc_index           = old->tc_index;
+        CHECK_SKB_FIELD(tc_index);
 #ifdef CONFIG_NET_CLS_ACT
-        new->tc_verd            = old->tc_verd;
+        CHECK_SKB_FIELD(tc_verd);
 #endif
 #endif
-        new->vlan_proto         = old->vlan_proto;
-        new->vlan_tci           = old->vlan_tci;
-
-        skb_copy_secmark(new, old);
 
-#ifdef CONFIG_NET_RX_BUSY_POLL
-        new->napi_id    = old->napi_id;
-#endif
 }
 
 /*
@@ -876,7 +879,6 @@ struct sk_buff *skb_clone(struct sk_buff *skb, gfp_t gfp_mask)
                         return NULL;
 
                 kmemcheck_annotate_bitfield(n, flags1);
-                kmemcheck_annotate_bitfield(n, flags2);
                 n->fclone = SKB_FCLONE_UNAVAILABLE;
         }