From: Arjun Roy <arjunroy@xxxxxxxxxx>
Use vm_insert_pages() for tcp receive zerocopy. Spin lock cycles
(as reported by perf) drop from a couple of percentage points
to a fraction of a percent. This results in a roughly 6% increase in
efficiency, measured roughly as zerocopy receive count divided by CPU
utilization.
The intention of this patch-set is to reduce atomic ops for
tcp zerocopy receives, which normally hits the same spinlock multiple
times consecutively.
Signed-off-by: Arjun Roy <arjunroy@xxxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: Soheil Hassas Yeganeh <soheil@xxxxxxxxxx>
---
net/ipv4/tcp.c | 67 +++++++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 61 insertions(+), 6 deletions(-)
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 34490d972758..52f96c3ceab3 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -1861,14 +1861,48 @@ int tcp_mmap(struct file *file, struct socket *sock,
}
EXPORT_SYMBOL(tcp_mmap);
+static int tcp_zerocopy_vm_insert_batch(struct vm_area_struct *vma,
+ struct page **pages,
+ unsigned long pages_to_map,
+ unsigned long *insert_addr,
+ u32 *length_with_pending,
+ u32 *seq,
+ struct tcp_zerocopy_receive *zc)
+{
+ unsigned long pages_remaining = pages_to_map;
+ int bytes_mapped;
+ int ret;
+
+ ret = vm_insert_pages(vma, *insert_addr, pages, &pages_remaining);
+ bytes_mapped = PAGE_SIZE * (pages_to_map - pages_remaining);
+ /* Even if vm_insert_pages fails, it may have partially succeeded in
+ * mapping (some but not all of the pages).
+ */
+ *seq += bytes_mapped;
+ *insert_addr += bytes_mapped;
+ if (ret) {
+ /* But if vm_insert_pages did fail, we have to unroll some state
+ * we speculatively touched before.
+ */
+ const int bytes_not_mapped = PAGE_SIZE * pages_remaining;
+ *length_with_pending -= bytes_not_mapped;
+ zc->recv_skip_hint += bytes_not_mapped;
+ }
+ return ret;
+}
+
static int tcp_zerocopy_receive(struct sock *sk,
struct tcp_zerocopy_receive *zc)
{
unsigned long address = (unsigned long)zc->address;
u32 length = 0, seq, offset, zap_len;
+ #define PAGE_BATCH_SIZE 8
+ struct page *pages[PAGE_BATCH_SIZE];
const skb_frag_t *frags = NULL;
struct vm_area_struct *vma;
struct sk_buff *skb = NULL;
+ unsigned long pg_idx = 0;
+ unsigned long curr_addr;
struct tcp_sock *tp;
int inq;
int ret;
@@ -1901,15 +1935,26 @@ static int tcp_zerocopy_receive(struct sock *sk,
zc->recv_skip_hint = zc->length;
}
ret = 0;
+ curr_addr = address;
while (length + PAGE_SIZE <= zc->length) {
if (zc->recv_skip_hint < PAGE_SIZE) {
+ /* If we're here, finish the current batch. */
+ if (pg_idx) {
+ ret = tcp_zerocopy_vm_insert_batch(vma, pages,
+ pg_idx,
+ &curr_addr,
+ &length,
+ &seq, zc);
+ if (ret)
+ goto out;
+ pg_idx = 0;
+ }
if (skb) {
skb = skb->next;
offset = seq - TCP_SKB_CB(skb)->seq;
} else {
skb = tcp_recv_skb(sk, seq, &offset);
}
-
zc->recv_skip_hint = skb->len - offset;
offset -= skb_headlen(skb);
if ((int)offset < 0 || skb_has_frag_list(skb))
@@ -1933,14 +1978,24 @@ static int tcp_zerocopy_receive(struct sock *sk,
zc->recv_skip_hint -= remaining;
break;
}
- ret = vm_insert_page(vma, address + length,
- skb_frag_page(frags));
- if (ret)
- break;
+ pages[pg_idx] = skb_frag_page(frags);
+ pg_idx++;
length += PAGE_SIZE;
- seq += PAGE_SIZE;
zc->recv_skip_hint -= PAGE_SIZE;
frags++;
+ if (pg_idx == PAGE_BATCH_SIZE) {
+ ret = tcp_zerocopy_vm_insert_batch(vma, pages, pg_idx,
+ &curr_addr, &length,
+ &seq, zc);
+ if (ret)
+ goto out;
+ pg_idx = 0;
+ }
+ }
+ if (pg_idx) {
+ ret = tcp_zerocopy_vm_insert_batch(vma, pages, pg_idx,
+ &curr_addr, &length, &seq,
+ zc);
}
out:
up_read(¤t->mm->mmap_sem);
--
2.25.0.rc1.283.g88dfdc4193-goog
