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Date: Sun, 28 Sep 2014 16:37:07 -0400 (EDT) From: David Miller <davem@...emloft.net> To: eric.dumazet@...il.com Cc: netdev@...r.kernel.org, ncardwell@...gle.com, ycheng@...gle.com, willemb@...gle.com Subject: Re: [PATCH net-next] tcp: change tcp_skb_pcount() location From: Eric Dumazet <eric.dumazet@...il.com> Date: Wed, 24 Sep 2014 04:11:22 -0700 > From: Eric Dumazet <edumazet@...gle.com> > > Our goal is to access no more than one cache line access per skb in > a write or receive queue when doing the various walks. > > After recent TCP_SKB_CB() reorganizations, it is almost done. > > Last part is tcp_skb_pcount() which currently uses > skb_shinfo(skb)->gso_segs, which is a terrible choice, because it needs > 3 cache lines in current kernel (skb->head, skb->end, and > shinfo->gso_segs are all in 3 different cache lines, far from skb->cb) > > This very simple patch reuses space currently taken by tcp_tw_isn > only in input path, as tcp_skb_pcount is only needed for skb stored in > write queue. > > This considerably speeds up tcp_ack(), granted we avoid shinfo->tx_flags > to get SKBTX_ACK_TSTAMP, which seems possible. > > This also speeds up all sack processing in general. > > This speeds up tcp_sendmsg() because it no longer has to access/dirty > shinfo. > > Signed-off-by: Eric Dumazet <edumazet@...gle.com> > --- > Note : This patch applies cleanly after "tcp: better TCP_SKB_CB layout" > patch serie. Also applied, thanks Eric. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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