[ovs-dev] [PATCH] datapath: Compute checksum while sending packets to userspace().
Jesse Gross
jesse at nicira.com
Fri Jun 18 21:48:57 UTC 2010
Currently we compute the checksums on packets being sent to
userspace first and then copy them to a userspace buffer. However,
these two operations can be combined for a significant savings
because the packet data only has to be loaded once. This also
allows GSO packets to save an extra copy.
This will likely have an impact on NIC-121 because it eliminates
the code path that triggers the issue. However, it is not a fix
for the root cause.
---
datapath/datapath.c | 164 +++++++++++++++++++++++++++++++++++++++++++-------
datapath/vport-gre.c | 2 +-
2 files changed, 142 insertions(+), 24 deletions(-)
diff --git a/datapath/datapath.c b/datapath/datapath.c
index 5907e81..491f98a 100644
--- a/datapath/datapath.c
+++ b/datapath/datapath.c
@@ -32,6 +32,7 @@
#include <asm/system.h>
#include <asm/div64.h>
#include <asm/bug.h>
+#include <asm/highmem.h>
#include <linux/netfilter_bridge.h>
#include <linux/netfilter_ipv4.h>
#include <linux/inetdevice.h>
@@ -743,24 +744,16 @@ queue_control_packets(struct sk_buff *skb, struct sk_buff_head *queue,
nskb = skb->next;
skb->next = NULL;
- if (skb->ip_summed == CHECKSUM_PARTIAL) {
-
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,22)
- /* Until 2.6.22, the start of the transport header was
- * also the start of data to be checksummed. Linux
- * 2.6.22 introduced the csum_start field for this
- * purpose, but we should point the transport header to
- * it anyway for backward compatibility, as
- * dev_queue_xmit() does even in 2.6.28. */
- skb_set_transport_header(skb, skb->csum_start -
- skb_headroom(skb));
+ /* Until 2.6.22, the start of the transport header was
+ * also the start of data to be checksummed. Linux
+ * 2.6.22 introduced the csum_start field for this
+ * purpose, but we should point the transport header to
+ * it anyway for backward compatibility, as
+ * dev_queue_xmit() does even in 2.6.28. */
+ skb_set_transport_header(skb, skb->csum_start - skb_headroom(skb));
#endif
- err = skb_checksum_help(skb);
- if (err)
- goto err_kfree_skbs;
- }
-
err = skb_cow(skb, sizeof *header);
if (err)
goto err_kfree_skbs;
@@ -810,7 +803,7 @@ dp_output_control(struct datapath *dp, struct sk_buff *skb, int queue_no,
/* Break apart GSO packets into their component pieces. Otherwise
* userspace may try to stuff a 64kB packet into a 1500-byte MTU. */
if (skb_is_gso(skb)) {
- struct sk_buff *nskb = skb_gso_segment(skb, 0);
+ struct sk_buff *nskb = skb_gso_segment(skb, NETIF_F_SG | NETIF_F_HW_CSUM);
if (nskb) {
kfree_skb(skb);
skb = nskb;
@@ -2067,6 +2060,100 @@ exit:
}
#endif
+/* Unfortunately this function is not exported so this is a verbatim copy
+ * from net/core/datagram.c in 2.6.30. */
+static int skb_copy_and_csum_datagram(const struct sk_buff *skb, int offset,
+ u8 __user *to, int len,
+ __wsum *csump)
+{
+ int start = skb_headlen(skb);
+ int pos = 0;
+ int i, copy = start - offset;
+
+ /* Copy header. */
+ if (copy > 0) {
+ int err = 0;
+ if (copy > len)
+ copy = len;
+ *csump = csum_and_copy_to_user(skb->data + offset, to, copy,
+ *csump, &err);
+ if (err)
+ goto fault;
+ if ((len -= copy) == 0)
+ return 0;
+ offset += copy;
+ to += copy;
+ pos = copy;
+ }
+
+ for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
+ int end;
+
+ WARN_ON(start > offset + len);
+
+ end = start + skb_shinfo(skb)->frags[i].size;
+ if ((copy = end - offset) > 0) {
+ __wsum csum2;
+ int err = 0;
+ u8 *vaddr;
+ skb_frag_t *frag = &skb_shinfo(skb)->frags[i];
+ struct page *page = frag->page;
+
+ if (copy > len)
+ copy = len;
+ vaddr = kmap(page);
+ csum2 = csum_and_copy_to_user(vaddr +
+ frag->page_offset +
+ offset - start,
+ to, copy, 0, &err);
+ kunmap(page);
+ if (err)
+ goto fault;
+ *csump = csum_block_add(*csump, csum2, pos);
+ if (!(len -= copy))
+ return 0;
+ offset += copy;
+ to += copy;
+ pos += copy;
+ }
+ start = end;
+ }
+
+ if (skb_shinfo(skb)->frag_list) {
+ struct sk_buff *list = skb_shinfo(skb)->frag_list;
+
+ for (; list; list=list->next) {
+ int end;
+
+ WARN_ON(start > offset + len);
+
+ end = start + list->len;
+ if ((copy = end - offset) > 0) {
+ __wsum csum2 = 0;
+ if (copy > len)
+ copy = len;
+ if (skb_copy_and_csum_datagram(list,
+ offset - start,
+ to, copy,
+ &csum2))
+ goto fault;
+ *csump = csum_block_add(*csump, csum2, pos);
+ if ((len -= copy) == 0)
+ return 0;
+ offset += copy;
+ to += copy;
+ pos += copy;
+ }
+ start = end;
+ }
+ }
+ if (!len)
+ return 0;
+
+fault:
+ return -EFAULT;
+}
+
ssize_t openvswitch_read(struct file *f, char __user *buf, size_t nbytes,
loff_t *ppos)
{
@@ -2075,8 +2162,7 @@ ssize_t openvswitch_read(struct file *f, char __user *buf, size_t nbytes,
int dp_idx = iminor(f->f_dentry->d_inode);
struct datapath *dp = get_dp(dp_idx);
struct sk_buff *skb;
- struct iovec __user iov;
- size_t copy_bytes;
+ size_t copy_bytes, tot_copy_bytes;
int retval;
if (!dp)
@@ -2111,12 +2197,44 @@ ssize_t openvswitch_read(struct file *f, char __user *buf, size_t nbytes,
}
}
success:
- copy_bytes = min_t(size_t, skb->len, nbytes);
- iov.iov_base = buf;
- iov.iov_len = copy_bytes;
- retval = skb_copy_datagram_iovec(skb, 0, &iov, iov.iov_len);
+ copy_bytes = tot_copy_bytes = min_t(size_t, skb->len, nbytes);
+
+ retval = 0;
+ if (skb->ip_summed == CHECKSUM_PARTIAL) {
+ __wsum csum = 0;
+ int csum_start, csum_offset;
+
+ csum_start = skb_transport_header(skb) - skb->data;
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,22)
+ csum_offset = skb->csum_offset;
+#else
+ csum_offset = skb->csum;
+#endif
+ if (csum_start + csum_offset + sizeof(__sum16) <= copy_bytes) {
+ retval = skb_copy_and_csum_datagram(skb, csum_start, buf + csum_start,
+ copy_bytes - csum_start, &csum);
+
+ if (!retval) {
+ __sum16 __user *csump;
+
+ copy_bytes = csum_start;
+ csump = (__sum16 __user *)(buf + csum_start + csum_offset);
+ put_user(csum_fold(csum), csump);
+ }
+ }
+ }
+
+ if (!retval) {
+ struct iovec __user iov;
+
+ iov.iov_base = buf;
+ iov.iov_len = copy_bytes;
+ retval = skb_copy_datagram_iovec(skb, 0, &iov, iov.iov_len);
+ }
+
if (!retval)
- retval = copy_bytes;
+ retval = tot_copy_bytes;
+
kfree_skb(skb);
error:
diff --git a/datapath/vport-gre.c b/datapath/vport-gre.c
index c71cc34..d4a5c5e 100644
--- a/datapath/vport-gre.c
+++ b/datapath/vport-gre.c
@@ -733,7 +733,7 @@ static struct sk_buff *
handle_gso(struct sk_buff *skb)
{
if (skb_is_gso(skb)) {
- struct sk_buff *nskb = skb_gso_segment(skb, NETIF_F_SG);
+ struct sk_buff *nskb = skb_gso_segment(skb, 0);
dev_kfree_skb(skb);
return nskb;
--
1.7.0.4
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