netdev - Re: [PATCH net-next 14/17] tcp: remove pointless .dsack code

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Date:	Mon, 2 Mar 2009 13:54:17 +0200 (EET)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	David Miller <davem@...emloft.net>
cc:	Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next 14/17] tcp: remove pointless .dsack code

On Mon, 2 Mar 2009, David Miller wrote:

> From: "Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
> Date: Sat, 28 Feb 2009 16:44:39 +0200
> 
> > From: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
> > 
> > In the pure assignment case, the earlier zeroing is
> > still in effect.
> > 
> > Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
> 
> I skipped this one.
> 
> These tests could be there to avoid dirtying a cacheline
> when unnecessary.  And so unless we can prove the condition
> always hits and we always do the write, we should keep
> the tests there.

We'll be dirty it anyway (not that I check), the first "real" statement
in tcp_rcv_established is:

	tp->rx_opt.saw_tstamp = 0;

...that'll land on the same dword. :-/

I suppose the blocks are there just because they had more complexity 
inside when they had to calculate the eff_sacks too (maybe it would
have been better to just remove them in that drop-patch so you would
have had less head-ache :-)).

Besides, it isn't very nice to have tx/rx or rx'es on different cpus 
anyway, no? 

-- 
 i.