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Message-Id: <20090616.225316.263195307.davem@davemloft.net>
Date: Tue, 16 Jun 2009 22:53:16 -0700 (PDT)
From: David Miller <davem@...emloft.net>
To: ilpo.jarvinen@...sinki.fi
Cc: john.dykstra1@...il.com, ben.lahaise@...erion.com,
netdev@...r.kernel.org
Subject: Re: lots of cpu time spent in skb_copy_bits() in net-next with
small mtu
From: "Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
Date: Wed, 17 Jun 2009 08:46:56 +0300 (EEST)
> While I took a very short view on it earlier I notice that handling of the
> case when head is at the last skb and tail is at the end of queue was
> changed (without mention in the commit message whether it was
> intentionally) in the Dave's change (we used to exit at skb == tail while
> we don't necessarily do that anymore but take the additional checks that
> are made inside the loop ub tcp_collapse()). It would be nice if Dave
> would split that kind of complex transformation into more easily
> verifiable changes, even if the intermediate form itself would not remain
> in the final form, as is it's rather hard to track it all :-).
>
> I'm not sure if that change is significant though as one might view it as
> the opposite, ie., that the previous was unintented early exit since we
> wouldn't collapse bloated skb in the end but who knows... ...But I'm yet
> to really _understand_ everything that is going on there.
Sorry, will be more careful in the future. :-)
Can we atleast verify that applying the following revert patch makes
the problem go away? (it's a combination revert of commits
2df9001edc382c331f338f45d259feeaa740c418 and
915219441d566f1da0caa0e262be49b666159e17).
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 17b89c5..0fb8b44 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -439,14 +439,12 @@ int tcp_ioctl(struct sock *sk, int cmd, unsigned long arg)
!tp->urg_data ||
before(tp->urg_seq, tp->copied_seq) ||
!before(tp->urg_seq, tp->rcv_nxt)) {
- struct sk_buff *skb;
-
answ = tp->rcv_nxt - tp->copied_seq;
/* Subtract 1, if FIN is in queue. */
- skb = skb_peek_tail(&sk->sk_receive_queue);
- if (answ && skb)
- answ -= tcp_hdr(skb)->fin;
+ if (answ && !skb_queue_empty(&sk->sk_receive_queue))
+ answ -=
+ tcp_hdr((struct sk_buff *)sk->sk_receive_queue.prev)->fin;
} else
answ = tp->urg_seq - tp->copied_seq;
release_sock(sk);
@@ -1384,7 +1382,11 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
/* Next get a buffer. */
- skb_queue_walk(&sk->sk_receive_queue, skb) {
+ skb = skb_peek(&sk->sk_receive_queue);
+ do {
+ if (!skb)
+ break;
+
/* Now that we have two receive queues this
* shouldn't happen.
*/
@@ -1401,7 +1403,8 @@ int tcp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
if (tcp_hdr(skb)->fin)
goto found_fin_ok;
WARN_ON(!(flags & MSG_PEEK));
- }
+ skb = skb->next;
+ } while (skb != (struct sk_buff *)&sk->sk_receive_queue);
/* Well, if we have backlog, try to process it now yet. */
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 2bdb0da..eeb8a92 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4426,7 +4426,7 @@ drop:
}
__skb_queue_head(&tp->out_of_order_queue, skb);
} else {
- struct sk_buff *skb1 = skb_peek_tail(&tp->out_of_order_queue);
+ struct sk_buff *skb1 = tp->out_of_order_queue.prev;
u32 seq = TCP_SKB_CB(skb)->seq;
u32 end_seq = TCP_SKB_CB(skb)->end_seq;
@@ -4443,18 +4443,15 @@ drop:
}
/* Find place to insert this segment. */
- while (1) {
+ do {
if (!after(TCP_SKB_CB(skb1)->seq, seq))
break;
- if (skb_queue_is_first(&tp->out_of_order_queue, skb1)) {
- skb1 = NULL;
- break;
- }
- skb1 = skb_queue_prev(&tp->out_of_order_queue, skb1);
- }
+ } while ((skb1 = skb1->prev) !=
+ (struct sk_buff *)&tp->out_of_order_queue);
/* Do skb overlap to previous one? */
- if (skb1 && before(seq, TCP_SKB_CB(skb1)->end_seq)) {
+ if (skb1 != (struct sk_buff *)&tp->out_of_order_queue &&
+ before(seq, TCP_SKB_CB(skb1)->end_seq)) {
if (!after(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
/* All the bits are present. Drop. */
__kfree_skb(skb);
@@ -4466,26 +4463,15 @@ drop:
tcp_dsack_set(sk, seq,
TCP_SKB_CB(skb1)->end_seq);
} else {
- if (skb_queue_is_first(&tp->out_of_order_queue,
- skb1))
- skb1 = NULL;
- else
- skb1 = skb_queue_prev(
- &tp->out_of_order_queue,
- skb1);
+ skb1 = skb1->prev;
}
}
- if (!skb1)
- __skb_queue_head(&tp->out_of_order_queue, skb);
- else
- __skb_queue_after(&tp->out_of_order_queue, skb1, skb);
+ __skb_queue_after(&tp->out_of_order_queue, skb1, skb);
/* And clean segments covered by new one as whole. */
- while (!skb_queue_is_last(&tp->out_of_order_queue, skb)) {
- skb1 = skb_queue_next(&tp->out_of_order_queue, skb);
-
- if (!after(end_seq, TCP_SKB_CB(skb1)->seq))
- break;
+ while ((skb1 = skb->next) !=
+ (struct sk_buff *)&tp->out_of_order_queue &&
+ after(end_seq, TCP_SKB_CB(skb1)->seq)) {
if (before(end_seq, TCP_SKB_CB(skb1)->end_seq)) {
tcp_dsack_extend(sk, TCP_SKB_CB(skb1)->seq,
end_seq);
@@ -4506,10 +4492,7 @@ add_sack:
static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
struct sk_buff_head *list)
{
- struct sk_buff *next = NULL;
-
- if (!skb_queue_is_last(list, skb))
- next = skb_queue_next(list, skb);
+ struct sk_buff *next = skb->next;
__skb_unlink(skb, list);
__kfree_skb(skb);
@@ -4520,9 +4503,6 @@ static struct sk_buff *tcp_collapse_one(struct sock *sk, struct sk_buff *skb,
/* Collapse contiguous sequence of skbs head..tail with
* sequence numbers start..end.
- *
- * If tail is NULL, this means until the end of the list.
- *
* Segments with FIN/SYN are not collapsed (only because this
* simplifies code)
*/
@@ -4531,23 +4511,15 @@ tcp_collapse(struct sock *sk, struct sk_buff_head *list,
struct sk_buff *head, struct sk_buff *tail,
u32 start, u32 end)
{
- struct sk_buff *skb, *n;
- bool end_of_skbs;
+ struct sk_buff *skb;
/* First, check that queue is collapsible and find
* the point where collapsing can be useful. */
- skb = head;
-restart:
- end_of_skbs = true;
- skb_queue_walk_from_safe(list, skb, n) {
- if (skb == tail)
- break;
+ for (skb = head; skb != tail;) {
/* No new bits? It is possible on ofo queue. */
if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
skb = tcp_collapse_one(sk, skb, list);
- if (!skb)
- break;
- goto restart;
+ continue;
}
/* The first skb to collapse is:
@@ -4557,24 +4529,16 @@ restart:
*/
if (!tcp_hdr(skb)->syn && !tcp_hdr(skb)->fin &&
(tcp_win_from_space(skb->truesize) > skb->len ||
- before(TCP_SKB_CB(skb)->seq, start))) {
- end_of_skbs = false;
+ before(TCP_SKB_CB(skb)->seq, start) ||
+ (skb->next != tail &&
+ TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb->next)->seq)))
break;
- }
-
- if (!skb_queue_is_last(list, skb)) {
- struct sk_buff *next = skb_queue_next(list, skb);
- if (next != tail &&
- TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(next)->seq) {
- end_of_skbs = false;
- break;
- }
- }
/* Decided to skip this, advance start seq. */
start = TCP_SKB_CB(skb)->end_seq;
+ skb = skb->next;
}
- if (end_of_skbs || tcp_hdr(skb)->syn || tcp_hdr(skb)->fin)
+ if (skb == tail || tcp_hdr(skb)->syn || tcp_hdr(skb)->fin)
return;
while (before(start, end)) {
@@ -4619,8 +4583,7 @@ restart:
}
if (!before(start, TCP_SKB_CB(skb)->end_seq)) {
skb = tcp_collapse_one(sk, skb, list);
- if (!skb ||
- skb == tail ||
+ if (skb == tail ||
tcp_hdr(skb)->syn ||
tcp_hdr(skb)->fin)
return;
@@ -4647,21 +4610,17 @@ static void tcp_collapse_ofo_queue(struct sock *sk)
head = skb;
for (;;) {
- struct sk_buff *next = NULL;
-
- if (!skb_queue_is_last(&tp->out_of_order_queue, skb))
- next = skb_queue_next(&tp->out_of_order_queue, skb);
- skb = next;
+ skb = skb->next;
/* Segment is terminated when we see gap or when
* we are at the end of all the queue. */
- if (!skb ||
+ if (skb == (struct sk_buff *)&tp->out_of_order_queue ||
after(TCP_SKB_CB(skb)->seq, end) ||
before(TCP_SKB_CB(skb)->end_seq, start)) {
tcp_collapse(sk, &tp->out_of_order_queue,
head, skb, start, end);
head = skb;
- if (!skb)
+ if (skb == (struct sk_buff *)&tp->out_of_order_queue)
break;
/* Start new segment */
start = TCP_SKB_CB(skb)->seq;
@@ -4722,11 +4681,10 @@ static int tcp_prune_queue(struct sock *sk)
tp->rcv_ssthresh = min(tp->rcv_ssthresh, 4U * tp->advmss);
tcp_collapse_ofo_queue(sk);
- if (!skb_queue_empty(&sk->sk_receive_queue))
- tcp_collapse(sk, &sk->sk_receive_queue,
- skb_peek(&sk->sk_receive_queue),
- NULL,
- tp->copied_seq, tp->rcv_nxt);
+ tcp_collapse(sk, &sk->sk_receive_queue,
+ sk->sk_receive_queue.next,
+ (struct sk_buff *)&sk->sk_receive_queue,
+ tp->copied_seq, tp->rcv_nxt);
sk_mem_reclaim(sk);
if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf)
--
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