Linux Virtualization - Nov 2013 - [PATCH net-next V3 2/2] virtio-net: coalesce rx frags when possible during rx

Sometimes we need to coalesce the rx frags to avoid frag list. One example is
virtio-net driver which tries to use small frags for both MTU sized packet and
GSO packet. So this patch introduce skb_coalesce_rx_frag() to do this.

Cc: Rusty Russell <rusty at rustcorp.com.au>
Cc: Michael S. Tsirkin <mst at redhat.com>
Cc: Michael Dalton <mwdalton at google.com>
Cc: Eric Dumazet <edumazet at google.com>
Acked-by: Michael S. Tsirkin <mst at redhat.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
Changes from V2:
- remove the skb_frag_unref() and let the called to put the page reference
Changes from V1:
- remove the useless off parameter.
---
 include/linux/skbuff.h |  3 +++
 net/core/skbuff.c      | 12 ++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 2c15497..fffaeaf 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1372,6 +1372,9 @@ static inline void skb_fill_page_desc(struct sk_buff *skb,
int i,
 void skb_add_rx_frag(struct sk_buff *skb, int i, struct page *page, int off,
 		     int size, unsigned int truesize);
 
+void skb_coalesce_rx_frag(struct sk_buff *skb, int i, int size,
+			  unsigned int truesize);
+
 #define SKB_PAGE_ASSERT(skb) 	BUG_ON(skb_shinfo(skb)->nr_frags)
 #define SKB_FRAG_ASSERT(skb) 	BUG_ON(skb_has_frag_list(skb))
 #define SKB_LINEAR_ASSERT(skb)  BUG_ON(skb_is_nonlinear(skb))
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 0ab32fa..a729b97 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -476,6 +476,18 @@ void skb_add_rx_frag(struct sk_buff *skb, int i, struct
page *page, int off,
 }
 EXPORT_SYMBOL(skb_add_rx_frag);
 
+void skb_coalesce_rx_frag(struct sk_buff *skb, int i, int size,
+			  unsigned int truesize)
+{
+	skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
+
+	skb_frag_size_add(frag, size);
+	skb->len += size;
+	skb->data_len += size;
+	skb->truesize += truesize;
+}
+EXPORT_SYMBOL(skb_coalesce_rx_frag);
+
 static void skb_drop_list(struct sk_buff **listp)
 {
 	kfree_skb_list(*listp);
-- 
1.8.1.2

Commit 2613af0ed18a11d5c566a81f9a6510b73180660a (virtio_net: migrate mergeable
rx buffers to page frag allocators) try to increase the payload/truesize for
MTU-sized traffic. But this will introduce the extra overhead for GSO packets
received because of the frag list. This commit tries to reduce this issue by
coalesce the possible rx frags when possible during rx. Test result shows the
about 15% improvement on full size GSO packet receiving (and even better than
before commit 2613af0ed18a11d5c566a81f9a6510b73180660a).

Before this commit:
./netperf -H 192.168.100.4
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.100.4
() port 0 AF_INET : demo
Recv   Send    Send
Socket Socket  Message  Elapsed
Size   Size    Size     Time     Throughput
bytes  bytes   bytes    secs.    10^6bits/sec

 87380  16384  16384    10.00    20303.87

After this commit:
./netperf -H 192.168.100.4
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.100.4
() port 0 AF_INET : demo
Recv   Send    Send
Socket Socket  Message  Elapsed
Size   Size    Size     Time     Throughput
bytes  bytes   bytes    secs.    10^6bits/sec

 87380  16384  16384    10.00    23841.26

Cc: Rusty Russell <rusty at rustcorp.com.au>
Cc: Michael S. Tsirkin <mst at redhat.com>
Cc: Michael Dalton <mwdalton at google.com>
Cc: Eric Dumazet <edumazet at google.com>
Acked-by: Michael S. Tsirkin <mst at redhat.com>
Acked-by: Eric Dumazet <edumazet at google.com>
Signed-off-by: Jason Wang <jasowang at redhat.com>
---
Changes from V2:
- call put_page() instead of depending on skb_coalesce_rx_frag()
---
 drivers/net/virtio_net.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 113ee93..50774ae 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -305,7 +305,7 @@ static int receive_mergeable(struct receive_queue *rq,
struct sk_buff *head_skb)
 	struct sk_buff *curr_skb = head_skb;
 	char *buf;
 	struct page *page;
-	int num_buf, len;
+	int num_buf, len, offset;
 
 	num_buf = hdr->mhdr.num_buffers;
 	while (--num_buf) {
@@ -342,9 +342,16 @@ static int receive_mergeable(struct receive_queue *rq,
struct sk_buff *head_skb)
 			head_skb->truesize += MAX_PACKET_LEN;
 		}
 		page = virt_to_head_page(buf);
-		skb_add_rx_frag(curr_skb, num_skb_frags, page,
-				buf - (char *)page_address(page), len,
-				MAX_PACKET_LEN);
+		offset = buf - (char *)page_address(page);
+		if (skb_can_coalesce(curr_skb, num_skb_frags, page, offset)) {
+			put_page(page);
+			skb_coalesce_rx_frag(curr_skb, num_skb_frags - 1,
+					     len, MAX_PACKET_LEN);
+		} else {
+			skb_add_rx_frag(curr_skb, num_skb_frags, page,
+					offset, len,
+					MAX_PACKET_LEN);
+		}
 		--rq->num;
 	}
 	return 0;
-- 
1.8.1.2

On Fri, 2013-11-01 at 14:07 +0800, Jason Wang wrote:
> Sometimes we need to coalesce the rx frags to avoid frag list. One example
is
> virtio-net driver which tries to use small frags for both MTU sized packet
and
> GSO packet. So this patch introduce skb_coalesce_rx_frag() to do this.
> 
> Cc: Rusty Russell <rusty at rustcorp.com.au>
> Cc: Michael S. Tsirkin <mst at redhat.com>
> Cc: Michael Dalton <mwdalton at google.com>
> Cc: Eric Dumazet <edumazet at google.com>
> Acked-by: Michael S. Tsirkin <mst at redhat.com>
> Signed-off-by: Jason Wang <jasowang at redhat.com>
> ---
> Changes from V2:
> - remove the skb_frag_unref() and let the called to put the page reference
> Changes from V1:
> - remove the useless off parameter.
> ---
Acked-by: Eric Dumazet <edumazet at google.com>

On Fri, 2013-11-01 at 14:07 +0800, Jason Wang wrote:
> Commit 2613af0ed18a11d5c566a81f9a6510b73180660a (virtio_net: migrate
mergeable
> rx buffers to page frag allocators) try to increase the payload/truesize
for
> MTU-sized traffic. But this will introduce the extra overhead for GSO
packets
> received because of the frag list. This commit tries to reduce this issue
by
> coalesce the possible rx frags when possible during rx. Test result shows
the
> about 15% improvement on full size GSO packet receiving (and even better
than
> before commit 2613af0ed18a11d5c566a81f9a6510b73180660a).
> 
> Before this commit:
> ./netperf -H 192.168.100.4
> MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to
192.168.100.4
> () port 0 AF_INET : demo
> Recv   Send    Send
> Socket Socket  Message  Elapsed
> Size   Size    Size     Time     Throughput
> bytes  bytes   bytes    secs.    10^6bits/sec
> 
>  87380  16384  16384    10.00    20303.87
> 
> After this commit:
> ./netperf -H 192.168.100.4
> MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to
192.168.100.4
> () port 0 AF_INET : demo
> Recv   Send    Send
> Socket Socket  Message  Elapsed
> Size   Size    Size     Time     Throughput
> bytes  bytes   bytes    secs.    10^6bits/sec
> 
>  87380  16384  16384    10.00    23841.26
> 
> Cc: Rusty Russell <rusty at rustcorp.com.au>
> Cc: Michael S. Tsirkin <mst at redhat.com>
> Cc: Michael Dalton <mwdalton at google.com>
> Cc: Eric Dumazet <edumazet at google.com>
> Acked-by: Michael S. Tsirkin <mst at redhat.com>
> Acked-by: Eric Dumazet <edumazet at google.com>
> Signed-off-by: Jason Wang <jasowang at redhat.com>
> ---
> Changes from V2:
> - call put_page() instead of depending on skb_coalesce_rx_frag()
> ---
Yes, very nice improvement, thanks again !

Acked-by: Eric Dumazet <edumazet at google.com>

From: Jason Wang <jasowang at redhat.com>
Date: Fri,  1 Nov 2013 14:07:47 +0800
> Sometimes we need to coalesce the rx frags to avoid frag list. One example
is
> virtio-net driver which tries to use small frags for both MTU sized packet
and
> GSO packet. So this patch introduce skb_coalesce_rx_frag() to do this.
> 
> Cc: Rusty Russell <rusty at rustcorp.com.au>
> Cc: Michael S. Tsirkin <mst at redhat.com>
> Cc: Michael Dalton <mwdalton at google.com>
> Cc: Eric Dumazet <edumazet at google.com>
> Acked-by: Michael S. Tsirkin <mst at redhat.com>
> Signed-off-by: Jason Wang <jasowang at redhat.com>
> ---
> Changes from V2:
> - remove the skb_frag_unref() and let the called to put the page reference
> Changes from V1:
> - remove the useless off parameter.
Applied.

From: Jason Wang <jasowang at redhat.com>
Date: Fri,  1 Nov 2013 14:07:48 +0800
> Commit 2613af0ed18a11d5c566a81f9a6510b73180660a (virtio_net: migrate
mergeable
> rx buffers to page frag allocators) try to increase the payload/truesize
for
> MTU-sized traffic. But this will introduce the extra overhead for GSO
packets
> received because of the frag list. This commit tries to reduce this issue
by
> coalesce the possible rx frags when possible during rx. Test result shows
the
> about 15% improvement on full size GSO packet receiving (and even better
than
> before commit 2613af0ed18a11d5c566a81f9a6510b73180660a).
...
> Cc: Rusty Russell <rusty at rustcorp.com.au>
> Cc: Michael S. Tsirkin <mst at redhat.com>
> Cc: Michael Dalton <mwdalton at google.com>
> Cc: Eric Dumazet <edumazet at google.com>
> Acked-by: Michael S. Tsirkin <mst at redhat.com>
> Acked-by: Eric Dumazet <edumazet at google.com>
> Signed-off-by: Jason Wang <jasowang at redhat.com>
> ---
> Changes from V2:
> - call put_page() instead of depending on skb_coalesce_rx_frag()
Looks fantastic, applied, thanks Jason!