Re: [Fwd: [Fwd: Is sendfile all that sexy? (fwd)]]

[Andrea Arcangeli <andrea@suse.de>]

On Sat, Jan 20, 2001 at 11:22:14PM +0300, kuznet@ms2.inr.ac.ru wrote:
> Hello!
> 
> > > 	write(100000*MSS)
> > > 	write(1)
> > > 	write(1)
> ...
> > As far as I can tell, the second "write(1)" will always merge with the
> > first one
> 
> This would be true, if Andrea wrote not exactly 100000*MSS,
> but 100000*MSS+1 or just write(<lots of data>).

So then this:

	val = 1
	setsockopt(TCP_CORK, &val) /* cork */

	write(100000*MSS+1)
	write(1)	

	val = 0
	setsockopt(TCP_CORK, &val) /* uncork */

is different from this:

	val = 1
	setsockopt(TCP_CORK, &val) /* cork */

	write(100000*MSS+1)
	write(1)	

	val = 0
	setsockopt(TCP_CORK, &val) /* uncork */

	val = 1
	setsockopt(TCP_NODELAY, &val)
	val = 0
	setsockopt(TCP_NODELAY, &val)

This was all my wondering about uncorking not being equivalent to SIOCPUSH.
(the two setsockopt(TCP_NODELAY) can be replaced with a SIOCPUSH of course)

If I understood wall they would been equivalent if I did write(100000*MSS)
instead of write(100000*MSS+1).

(and btw, the TCP_NODELAY being cleared immediatly means that if the last
packet can't be sent during the setsockopt it will be delayed with nagle as
usual when we get the acknowledgments from the receiver, that's the same
mistake of my SIOCPUSH first implementation that infact should be sligtly
improved in the way descriped a few emails ago adding a tp->push field and
then it will become different than going for a moment in TCP_NODELAY mode)

Andrea
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