net: __alloc_skb() speedup
With following patch I can reach maximum rate of my pktgen+udpsink
simulator :
- 'old' machine : dual quad core E5450 @3.00GHz
- 64 UDP rx flows (only differ by destination port)
- RPS enabled, NIC interrupts serviced on cpu0
- rps dispatched on 7 other cores. (~130.000 IPI per second)
- SLAB allocator (faster than SLUB in this workload)
- tg3 NIC
- 1.080.000 pps without a single drop at NIC level.
Idea is to add two prefetchw() calls in __alloc_skb(), one to prefetch
first sk_buff cache line, the second to prefetch the shinfo part.
Also using one memset() to initialize all skb_shared_info fields instead
of one by one to reduce number of instructions, using long word moves.
All skb_shared_info fields before 'dataref' are cleared in
__alloc_skb().
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 746a652..88d5539 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -187,7 +187,6 @@
* the end of the header data, ie. at skb->end.
*/
struct skb_shared_info {
- atomic_t dataref;
unsigned short nr_frags;
unsigned short gso_size;
/* Warning: this field is not always filled in (UFO)! */
@@ -197,6 +196,12 @@
union skb_shared_tx tx_flags;
struct sk_buff *frag_list;
struct skb_shared_hwtstamps hwtstamps;
+
+ /*
+ * Warning : all fields before dataref are cleared in __alloc_skb()
+ */
+ atomic_t dataref;
+
skb_frag_t frags[MAX_SKB_FRAGS];
/* Intermediate layers must ensure that destructor_arg
* remains valid until skb destructor */
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 8b9c109..a9b0e1f 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -181,12 +181,14 @@
skb = kmem_cache_alloc_node(cache, gfp_mask & ~__GFP_DMA, node);
if (!skb)
goto out;
+ prefetchw(skb);
size = SKB_DATA_ALIGN(size);
data = kmalloc_node_track_caller(size + sizeof(struct skb_shared_info),
gfp_mask, node);
if (!data)
goto nodata;
+ prefetchw(data + size);
/*
* Only clear those fields we need to clear, not those that we will
@@ -208,15 +210,8 @@
/* make sure we initialize shinfo sequentially */
shinfo = skb_shinfo(skb);
+ memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
atomic_set(&shinfo->dataref, 1);
- shinfo->nr_frags = 0;
- shinfo->gso_size = 0;
- shinfo->gso_segs = 0;
- shinfo->gso_type = 0;
- shinfo->ip6_frag_id = 0;
- shinfo->tx_flags.flags = 0;
- skb_frag_list_init(skb);
- memset(&shinfo->hwtstamps, 0, sizeof(shinfo->hwtstamps));
if (fclone) {
struct sk_buff *child = skb + 1;
@@ -505,16 +500,10 @@
return 0;
skb_release_head_state(skb);
+
shinfo = skb_shinfo(skb);
+ memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
atomic_set(&shinfo->dataref, 1);
- shinfo->nr_frags = 0;
- shinfo->gso_size = 0;
- shinfo->gso_segs = 0;
- shinfo->gso_type = 0;
- shinfo->ip6_frag_id = 0;
- shinfo->tx_flags.flags = 0;
- skb_frag_list_init(skb);
- memset(&shinfo->hwtstamps, 0, sizeof(shinfo->hwtstamps));
memset(skb, 0, offsetof(struct sk_buff, tail));
skb->data = skb->head + NET_SKB_PAD;