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Date: Tue, 6 Dec 2011 11:57:14 +0000
From: Ian Campbell <Ian.Campbell@...rix.com>
To: David Miller <davem@...emloft.net>
CC: Jesse Brandeburg <jesse.brandeburg@...el.com>,
<netdev@...r.kernel.org>
Subject: Re: [PATCH 0/4] skb paged fragment destructors
On Wed, 2011-11-09 at 15:01 +0000, Ian Campbell wrote:
> * split linear data allocation and shinfo allocation into two. I
> suspect this will have its own performance implications? On the
> positive side skb_shared_info could come from its own fixed size
> pool/cache which might have some benefits
I played with this to see how it would look. Illustrative patch below.
I figure that lots of small frames is the interesting workload for a
change such as this but I don't know if iperf is necessarily the best
benchmark for measuring that.
Before changing things I got:
iperf -c qarun -m -t 60 -u -b 10000M -l 64
------------------------------------------------------------
Client connecting to qarun, UDP port 5001
Sending 64 byte datagrams
UDP buffer size: 224 KByte (default)
------------------------------------------------------------
[ 3] local 10.80.225.63 port 45857 connected with 10.80.224.22 port 5001
[ ID] Interval Transfer Bandwidth
[ 3] 0.0-60.0 sec 844 MBytes 118 Mbits/sec
[ 3] Sent 13820376 datagrams
[ 3] Server Report:
[ 3] 0.0-60.0 sec 844 MBytes 118 Mbits/sec 0.005 ms 0/13820375 (0%)
[ 3] 0.0-60.0 sec 1 datagrams received out-of-order
whereas with the patch:
# iperf -c qarun -m -t 60 -u -b 10000M -l 64
------------------------------------------------------------
Client connecting to qarun, UDP port 5001
Sending 64 byte datagrams
UDP buffer size: 224 KByte (default)
------------------------------------------------------------
[ 3] local 10.80.225.63 port 42504 connected with 10.80.224.22 port 5001
[ ID] Interval Transfer Bandwidth
[ 3] 0.0-60.0 sec 833 MBytes 116 Mbits/sec
[ 3] Sent 13645857 datagrams
[ 3] Server Report:
[ 3] 0.0-60.0 sec 833 MBytes 116 Mbits/sec 0.005 ms 0/13645856 (0%)
[ 3] 0.0-60.0 sec 1 datagrams received out-of-order
With 1200 byte datagrams I get basically identical throughput.
(nb: none of the skb destructor stuff was present in either case)
> * steal a bit a pointer to indicate destructor pointer vs regular
> struct page pointer (moving the struct page into the destructor
> datastructure for that case). Stops us sharing a single
> destructor between multiple pages, but that isn't critical
I also implemented this and compared to the above the patch is pretty
fugly, especially its impact on the SUNRPC patches to actually use the
feature. It needs a bit more cleanup before I can post it for comparison
though.
Ian.
drivers/net/ethernet/broadcom/bnx2.c | 5 +-
drivers/net/ethernet/broadcom/bnx2x/bnx2x.h | 4 +-
drivers/net/ethernet/broadcom/tg3.c | 3 +-
include/linux/skbuff.h | 9 ++-
net/core/skbuff.c | 67 ++++++++++++++++----------
5 files changed, 51 insertions(+), 37 deletions(-)
diff --git a/drivers/net/ethernet/broadcom/bnx2.c b/drivers/net/ethernet/broadcom/bnx2.c
index 83d8cef..4e37e05 100644
--- a/drivers/net/ethernet/broadcom/bnx2.c
+++ b/drivers/net/ethernet/broadcom/bnx2.c
@@ -5320,8 +5320,7 @@ bnx2_set_rx_ring_size(struct bnx2 *bp, u32 size)
/* 8 for CRC and VLAN */
rx_size = bp->dev->mtu + ETH_HLEN + BNX2_RX_OFFSET + 8;
- rx_space = SKB_DATA_ALIGN(rx_size + BNX2_RX_ALIGN) + NET_SKB_PAD +
- SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+ rx_space = SKB_DATA_ALIGN(rx_size + BNX2_RX_ALIGN) + NET_SKB_PAD;
bp->rx_copy_thresh = BNX2_RX_COPY_THRESH;
bp->rx_pg_ring_size = 0;
@@ -5345,7 +5344,7 @@ bnx2_set_rx_ring_size(struct bnx2 *bp, u32 size)
bp->rx_buf_use_size = rx_size;
/* hw alignment + build_skb() overhead*/
bp->rx_buf_size = SKB_DATA_ALIGN(bp->rx_buf_use_size + BNX2_RX_ALIGN) +
- NET_SKB_PAD + SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+ NET_SKB_PAD;
bp->rx_jumbo_thresh = rx_size - BNX2_RX_OFFSET;
bp->rx_ring_size = size;
bp->rx_max_ring = bnx2_find_max_ring(size, MAX_RX_RINGS);
diff --git a/drivers/net/ethernet/broadcom/bnx2x/bnx2x.h b/drivers/net/ethernet/broadcom/bnx2x/bnx2x.h
index 0f7b7a4..b3de327 100644
--- a/drivers/net/ethernet/broadcom/bnx2x/bnx2x.h
+++ b/drivers/net/ethernet/broadcom/bnx2x/bnx2x.h
@@ -1203,9 +1203,7 @@ struct bnx2x {
*/
#define BNX2X_FW_RX_ALIGN_START (1UL << BNX2X_RX_ALIGN_SHIFT)
-#define BNX2X_FW_RX_ALIGN_END \
- max(1UL << BNX2X_RX_ALIGN_SHIFT, \
- SKB_DATA_ALIGN(sizeof(struct skb_shared_info)))
+#define BNX2X_FW_RX_ALIGN_END (1UL << BNX2X_RX_ALIGN_SHIFT)
#define BNX2X_PXP_DRAM_ALIGN (BNX2X_RX_ALIGN_SHIFT - 5)
diff --git a/drivers/net/ethernet/broadcom/tg3.c b/drivers/net/ethernet/broadcom/tg3.c
index d9e9c8c..dbea57b 100644
--- a/drivers/net/ethernet/broadcom/tg3.c
+++ b/drivers/net/ethernet/broadcom/tg3.c
@@ -5426,8 +5426,7 @@ static int tg3_alloc_rx_data(struct tg3 *tp, struct tg3_rx_prodring_set *tpr,
* Callers depend upon this behavior and assume that
* we leave everything unchanged if we fail.
*/
- skb_size = SKB_DATA_ALIGN(data_size + TG3_RX_OFFSET(tp)) +
- SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+ skb_size = SKB_DATA_ALIGN(data_size + TG3_RX_OFFSET(tp));
data = kmalloc(skb_size, GFP_ATOMIC);
if (!data)
return -ENOMEM;
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 09b7ea5..48e91a0 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -40,8 +40,7 @@
#define SKB_DATA_ALIGN(X) (((X) + (SMP_CACHE_BYTES - 1)) & \
~(SMP_CACHE_BYTES - 1))
-#define SKB_WITH_OVERHEAD(X) \
- ((X) - SKB_DATA_ALIGN(sizeof(struct skb_shared_info)))
+#define SKB_WITH_OVERHEAD(X) ((X))
#define SKB_MAX_ORDER(X, ORDER) \
SKB_WITH_OVERHEAD((PAGE_SIZE << (ORDER)) - (X))
#define SKB_MAX_HEAD(X) (SKB_MAX_ORDER((X), 0))
@@ -476,6 +475,7 @@ struct sk_buff {
sk_buff_data_t end;
unsigned char *head,
*data;
+ struct skb_shared_info *shinfo;
unsigned int truesize;
atomic_t users;
};
@@ -634,7 +634,10 @@ static inline unsigned char *skb_end_pointer(const struct sk_buff *skb)
#endif
/* Internal */
-#define skb_shinfo(SKB) ((struct skb_shared_info *)(skb_end_pointer(SKB)))
+static inline struct skb_shared_info *skb_shinfo(const struct sk_buff *skb)
+{
+ return skb->shinfo;
+}
static inline struct skb_shared_hwtstamps *skb_hwtstamps(struct sk_buff *skb)
{
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 7dc05ec..cfbe8e5 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -73,6 +73,7 @@
static struct kmem_cache *skbuff_head_cache __read_mostly;
static struct kmem_cache *skbuff_fclone_cache __read_mostly;
+static struct kmem_cache *skbuff_shinfo_cache __read_mostly;
static void sock_pipe_buf_release(struct pipe_inode_info *pipe,
struct pipe_buffer *buf)
@@ -118,7 +119,7 @@ static const struct pipe_buf_operations sock_pipe_buf_ops = {
*
* Out of line support code for skb_put(). Not user callable.
*/
-static void skb_over_panic(struct sk_buff *skb, int sz, void *here)
+static void skb_over_panic(struct sk_buff*skb, int sz, void *here)
{
printk(KERN_EMERG "skb_over_panic: text:%p len:%d put:%d head:%p "
"data:%p tail:%#lx end:%#lx dev:%s\n",
@@ -184,22 +185,21 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
goto out;
prefetchw(skb);
+ shinfo = kmem_cache_alloc_node(skbuff_shinfo_cache,
+ gfp_mask & ~__GFP_DMA, node);
+ if (!shinfo)
+ goto noshinfo;
+ prefetchw(shinfo);
+
/* We do our best to align skb_shared_info on a separate cache
* line. It usually works because kmalloc(X > SMP_CACHE_BYTES) gives
* aligned memory blocks, unless SLUB/SLAB debug is enabled.
* Both skb->head and skb_shared_info are cache line aligned.
*/
size = SKB_DATA_ALIGN(size);
- size += SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
data = kmalloc_node_track_caller(size, gfp_mask, node);
if (!data)
goto nodata;
- /* kmalloc(size) might give us more room than requested.
- * Put skb_shared_info exactly at the end of allocated zone,
- * to allow max possible filling before reallocation.
- */
- size = SKB_WITH_OVERHEAD(ksize(data));
- prefetchw(data + size);
/*
* Only clear those fields we need to clear, not those that we will
@@ -210,6 +210,7 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
/* Account for allocated memory : skb + skb->head */
skb->truesize = SKB_TRUESIZE(size);
atomic_set(&skb->users, 1);
+ skb->shinfo = shinfo;
skb->head = data;
skb->data = data;
skb_reset_tail_pointer(skb);
@@ -219,7 +220,7 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
#endif
/* make sure we initialize shinfo sequentially */
- shinfo = skb_shinfo(skb);
+ BUG_ON(shinfo != skb_shinfo(skb));
memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
atomic_set(&shinfo->dataref, 1);
kmemcheck_annotate_variable(shinfo->destructor_arg);
@@ -238,6 +239,8 @@ struct sk_buff *__alloc_skb(unsigned int size, gfp_t gfp_mask,
out:
return skb;
nodata:
+ kmem_cache_free(skbuff_shinfo_cache, shinfo);
+noshinfo:
kmem_cache_free(cache, skb);
skb = NULL;
goto out;
@@ -254,8 +257,8 @@ EXPORT_SYMBOL(__alloc_skb);
* On a failure the return is %NULL, and @data is not freed.
* Notes :
* Before IO, driver allocates only data buffer where NIC put incoming frame
- * Driver should add room at head (NET_SKB_PAD) and
- * MUST add room at tail (SKB_DATA_ALIGN(skb_shared_info))
+ * Driver should add room at head (NET_SKB_PAD) and need not
+ * add room at tail (SKB_DATA_ALIGN(skb_shared_info))
* After IO, driver calls build_skb(), to allocate sk_buff and populate it
* before giving packet to stack.
* RX rings only contains data buffers, not full skbs.
@@ -270,11 +273,17 @@ struct sk_buff *build_skb(void *data)
if (!skb)
return NULL;
- size = ksize(data) - SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+ shinfo = kmem_cache_alloc(skbuff_shinfo_cache, GFP_ATOMIC);
+ if (!shinfo)
+ goto noshinfo;
+ prefetchw(shinfo);
+
+ size = ksize(data);
memset(skb, 0, offsetof(struct sk_buff, tail));
skb->truesize = SKB_TRUESIZE(size);
atomic_set(&skb->users, 1);
+ skb->shinfo = shinfo;
skb->head = data;
skb->data = data;
skb_reset_tail_pointer(skb);
@@ -284,12 +293,17 @@ struct sk_buff *build_skb(void *data)
#endif
/* make sure we initialize shinfo sequentially */
- shinfo = skb_shinfo(skb);
+ BUG_ON(shinfo != skb_shinfo(skb));
memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
atomic_set(&shinfo->dataref, 1);
kmemcheck_annotate_variable(shinfo->destructor_arg);
+out:
return skb;
+noshinfo:
+ kmem_cache_free(skbuff_head_cache, skb);
+ skb = NULL;
+ goto out;
}
EXPORT_SYMBOL(build_skb);
@@ -378,7 +392,7 @@ static void skb_clone_fraglist(struct sk_buff *skb)
skb_get(list);
}
-static void skb_release_data(struct sk_buff *skb)
+static void skb_release_data(struct sk_buff *skb, int free_shinfo)
{
if (!skb->cloned ||
!atomic_sub_return(skb->nohdr ? (1 << SKB_DATAREF_SHIFT) + 1 : 1,
@@ -404,6 +418,8 @@ static void skb_release_data(struct sk_buff *skb)
if (skb_has_frag_list(skb))
skb_drop_fraglist(skb);
+ if (free_shinfo)
+ kmem_cache_free(skbuff_shinfo_cache, skb_shinfo(skb));
kfree(skb->head);
}
}
@@ -474,7 +490,7 @@ static void skb_release_head_state(struct sk_buff *skb)
static void skb_release_all(struct sk_buff *skb)
{
skb_release_head_state(skb);
- skb_release_data(skb);
+ skb_release_data(skb, 1);
}
/**
@@ -646,6 +662,7 @@ static struct sk_buff *__skb_clone(struct sk_buff *n, struct sk_buff *skb)
C(tail);
C(end);
C(head);
+ C(shinfo);
C(data);
C(truesize);
atomic_set(&n->users, 1);
@@ -941,18 +958,14 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
fastpath = atomic_read(&skb_shinfo(skb)->dataref) == delta;
}
- if (fastpath &&
- size + sizeof(struct skb_shared_info) <= ksize(skb->head)) {
- memmove(skb->head + size, skb_shinfo(skb),
- offsetof(struct skb_shared_info,
- frags[skb_shinfo(skb)->nr_frags]));
+ if (fastpath && size <= ksize(skb->head)) {
memmove(skb->head + nhead, skb->head,
skb_tail_pointer(skb) - skb->head);
off = nhead;
goto adjust_others;
}
- data = kmalloc(size + sizeof(struct skb_shared_info), gfp_mask);
+ data = kmalloc(size, gfp_mask);
if (!data)
goto nodata;
@@ -961,10 +974,6 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
*/
memcpy(data + nhead, skb->head, skb_tail_pointer(skb) - skb->head);
- memcpy((struct skb_shared_info *)(data + size),
- skb_shinfo(skb),
- offsetof(struct skb_shared_info, frags[skb_shinfo(skb)->nr_frags]));
-after apply
if (fastpath) {
kfree(skb->head);
} else {
@@ -979,7 +988,7 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
if (skb_has_frag_list(skb))
skb_clone_fraglist(skb);
- skb_release_data(skb);
+ skb_release_data(skb, 0);
}
off = (data + nhead) - skb->head;
@@ -2956,6 +2965,12 @@ void __init skb_init(void)
0,
SLAB_HWCACHE_ALIGN|SLAB_PANIC,
NULL);
+
+ skbuff_shinfo_cache = kmem_cache_create("skbuff_shinfo_cache",
+ sizeof(struct skb_shared_info),
+ 0,
+ SLAB_HWCACHE_ALIGN|SLAB_PANIC,
+ NULL);
}
/**
--
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