Discovered that network stack were hitting the kmem_cache/SLUB
slowpath when freeing SKBs. Doing bulk free with kmem_cache_free_bulk
can speedup this slowpath.
NAPI context is a bit special, lets take advantage of that for bulk
free'ing SKBs.
In NAPI context we are running in softirq, which gives us certain
protection. A softirq can run on several CPUs at once. BUT the
important part is a softirq will never preempt another softirq running
on the same CPU. This gives us the opportunity to access per-cpu
variables in softirq context.
Extend napi_alloc_cache (before only contained page_frag_cache) to be
a struct with a small array based stack for holding SKBs. Introduce a
SKB defer and flush API for accessing this.
Introduce napi_consume_skb() as replacement for e.g. dev_consume_skb_any()
when running in NAPI context. A small trick to handle/detect if we
are called from netpoll is to see if budget is 0. In that case, we
need to invoke dev_consume_skb_irq().
Joint work with Alexander Duyck.
Signed-off-by: Jesper Dangaard Brouer <bro...@redhat.com>
Signed-off-by: Alexander Duyck <alexander.h.du...@redhat.com>
---
include/linux/skbuff.h | 3 ++
net/core/dev.c | 1 +
net/core/skbuff.c | 83 +++++++++++++++++++++++++++++++++++++++++++++---
3 files changed, 81 insertions(+), 6 deletions(-)
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 4398411236f1..a3dec82e0e2c 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -2308,6 +2308,9 @@ static inline struct sk_buff *napi_alloc_skb(struct
napi_struct *napi,
{
return __napi_alloc_skb(napi, length, GFP_ATOMIC);
}
+void napi_consume_skb(struct sk_buff *skb, int budget);
+
+void __kfree_skb_flush(void);
/**
* __dev_alloc_pages - allocate page for network Rx
diff --git a/net/core/dev.c b/net/core/dev.c
index 1225b4be8ed6..204059f67154 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4841,6 +4841,7 @@ static void net_rx_action(struct softirq_action *h)
}
}
+ __kfree_skb_flush();
local_irq_disable();
list_splice_tail_init(&sd->poll_list, &list);
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index fab4599ba8b2..2682ac46d640 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -347,8 +347,16 @@ struct sk_buff *build_skb(void *data, unsigned int
frag_size)
}
EXPORT_SYMBOL(build_skb);
+#define NAPI_SKB_CACHE_SIZE 64
+
+struct napi_alloc_cache {
+ struct page_frag_cache page;
+ size_t skb_count;
+ void *skb_cache[NAPI_SKB_CACHE_SIZE];
+};
+
static DEFINE_PER_CPU(struct page_frag_cache, netdev_alloc_cache);
-static DEFINE_PER_CPU(struct page_frag_cache, napi_alloc_cache);
+static DEFINE_PER_CPU(struct napi_alloc_cache, napi_alloc_cache);
static void *__netdev_alloc_frag(unsigned int fragsz, gfp_t gfp_mask)
{
@@ -378,9 +386,9 @@ EXPORT_SYMBOL(netdev_alloc_frag);
static void *__napi_alloc_frag(unsigned int fragsz, gfp_t gfp_mask)
{
- struct page_frag_cache *nc = this_cpu_ptr(&napi_alloc_cache);
+ struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
- return __alloc_page_frag(nc, fragsz, gfp_mask);
+ return __alloc_page_frag(&nc->page, fragsz, gfp_mask);
}
void *napi_alloc_frag(unsigned int fragsz)
@@ -474,7 +482,7 @@ EXPORT_SYMBOL(__netdev_alloc_skb);
struct sk_buff *__napi_alloc_skb(struct napi_struct *napi, unsigned int len,
gfp_t gfp_mask)
{
- struct page_frag_cache *nc = this_cpu_ptr(&napi_alloc_cache);
+ struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
struct sk_buff *skb;
void *data;
@@ -494,7 +502,7 @@ struct sk_buff *__napi_alloc_skb(struct napi_struct *napi,
unsigned int len,
if (sk_memalloc_socks())
gfp_mask |= __GFP_MEMALLOC;
- data = __alloc_page_frag(nc, len, gfp_mask);
+ data = __alloc_page_frag(&nc->page, len, gfp_mask);
if (unlikely(!data))
return NULL;
@@ -505,7 +513,7 @@ struct sk_buff *__napi_alloc_skb(struct napi_struct *napi,
unsigned int len,
}
/* use OR instead of assignment to avoid clearing of bits in mask */
- if (nc->pfmemalloc)
+ if (nc->page.pfmemalloc)
skb->pfmemalloc = 1;
skb->head_frag = 1;
@@ -747,6 +755,69 @@ void consume_skb(struct sk_buff *skb)
}
EXPORT_SYMBOL(consume_skb);
+void __kfree_skb_flush(void)
+{
+ struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
+
+ /* flush skb_cache if containing objects */
+ if (nc->skb_count) {
+ kmem_cache_free_bulk(skbuff_head_cache, nc->skb_count,
+ nc->skb_cache);
+ nc->skb_count = 0;
+ }
+}
+
+static void __kfree_skb_defer(struct sk_buff *skb)
+{
+ struct napi_alloc_cache *nc = this_cpu_ptr(&napi_alloc_cache);
+
+ /* drop skb->head and call any destructors for packet */
+ skb_release_all(skb);
+
+ /* record skb to CPU local list */
+ nc->skb_cache[nc->skb_count++] = skb;
+
+#ifdef CONFIG_SLUB
+ /* SLUB writes into objects when freeing */
+ prefetchw(skb);
+#endif
+
+ /* flush skb_cache if it is filled */
+ if (unlikely(nc->skb_count == NAPI_SKB_CACHE_SIZE)) {
+ kmem_cache_free_bulk(skbuff_head_cache, NAPI_SKB_CACHE_SIZE,
+ nc->skb_cache);
+ nc->skb_count = 0;
+ }
+}
+
+void napi_consume_skb(struct sk_buff *skb, int budget)
+{
+ if (unlikely(!skb))
+ return;
+
+ /* if budget is 0 assume netpoll w/ IRQs disabled */
+ if (unlikely(!budget)) {
+ dev_consume_skb_irq(skb);
+ return;
+ }
+
+ if (likely(atomic_read(&skb->users) == 1))
+ smp_rmb();
+ else if (likely(!atomic_dec_and_test(&skb->users)))
+ return;
+ /* if reaching here SKB is ready to free */
+ trace_consume_skb(skb);
+
+ /* if SKB is a clone, don't handle this case */
+ if (unlikely(skb->fclone != SKB_FCLONE_UNAVAILABLE)) {
+ __kfree_skb(skb);
+ return;
+ }
+
+ __kfree_skb_defer(skb);
+}
+EXPORT_SYMBOL(napi_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) < \
--
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