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Date: Wed, 7 May 2008 11:54:01 -0700 From: "Jerry Chu" <hkchu@...gle.com> To: "David Miller" <davem@...emloft.net> Cc: netdev@...r.kernel.org Subject: Re: Socket buffer sizes with autotuning On Tue, May 6, 2008 at 9:28 PM, David Miller <davem@...emloft.net> wrote: > From: "Jerry Chu" <hkchu@...gle.com> > > Date: Tue, 6 May 2008 20:57:46 -0700 > > > > It may be getting a copy (e.g., when GSO is on?) hence losing all > > its connection to the original tp and any chance to have the pkt > > properly accounted for as host_infligh by TCP. The skb may also be > > cloned more than once (e.g., due to tcpdump)... > > It only gets a copy if the SKB is already cloned and that clone is > alive somewhere (f.e. stuck in the device, a rare occurance by > the time we retransmit). This is one of many things about skb that I still don't completely understand. Why in tcp_transmit_skb() we'll have to pskb_copy() if skb_cloned()? Can't we clone a skb mulitple times? Is it due to some special optimization from skb->fclone stuff... that imposes this restriction? > > It is a clone %99.999999 of the time. When I turned on GSO but not TSO, I believe it's a copy %99.999999 of the time. (I must confess I don't understand GSO code yet. I temporarily ran out of stream after studying bunch of other code.) Jerry > -- 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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