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Date: Sun, 3 Apr 2022 14:06:29 +0100 From: Pavel Begunkov <asml.silence@...il.com> To: netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org> Cc: Eric Dumazet <edumazet@...gle.com>, Wei Liu <wei.liu@...nel.org>, Paul Durrant <paul@....org>, Pavel Begunkov <asml.silence@...il.com> Subject: [PATCH net-next 17/27] tcp: optimise skb_zerocopy_iter_stream() It's expensive to make a copy of 40B struct iov_iter to the point it was taking 0.2-0.5% of all cycles in my tests. iov_iter_revert() should be fine as it's a simple case without nested reverts/truncates. Signed-off-by: Pavel Begunkov <asml.silence@...il.com> --- net/core/skbuff.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 65ac779eb5cd..77cbdb02e885 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -1343,7 +1343,6 @@ int skb_zerocopy_iter_stream(struct sock *sk, struct sk_buff *skb, struct msghdr *msg, int len, struct ubuf_info *uarg) { - struct iov_iter orig_iter = msg->msg_iter; int err, orig_len = skb->len; /* An skb can only point to one uarg. This edge case happens when @@ -1357,7 +1356,7 @@ int skb_zerocopy_iter_stream(struct sock *sk, struct sk_buff *skb, struct sock *save_sk = skb->sk; /* Streams do not free skb on error. Reset to prev state. */ - msg->msg_iter = orig_iter; + iov_iter_revert(&msg->msg_iter, skb->len - orig_len); skb->sk = sk; ___pskb_trim(skb, orig_len); skb->sk = save_sk; -- 2.35.1
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