From: Eric Dumazet <eric.duma...@gmail.com> Date: Mon, 05 Dec 2016 09:57:19 -0800
> From: Eric Dumazet <eduma...@google.com> > > In UDP recvmsg() path we currently access 3 cache lines from an skb > while holding receive queue lock, plus another one if packet is > dequeued, since we need to change skb->next->prev > > 1st cache line (contains ->next/prev pointers, offsets 0x00 and 0x08) > 2nd cache line (skb->len & skb->peeked, offsets 0x80 and 0x8e) > 3rd cache line (skb->truesize/users, offsets 0xe0 and 0xe4) > > skb->peeked is only needed to make sure 0-length packets are properly > handled while MSG_PEEK is operated. > > I had first the intent to remove skb->peeked but the "MSG_PEEK at > non-zero offset" support added by Sam Kumar makes this not possible. > > This patch avoids one cache line miss during the locked section, when > skb->len and skb->peeked do not have to be read. > > It also avoids the skb_set_peeked() cost for non empty UDP datagrams. > > Signed-off-by: Eric Dumazet <eduma...@google.com> Applied, thanks Eric.
