Re: [net-next PATCH v4 2/3] net: TCP thin linear timeouts

[Franco Fichtner]

Hi,

Andreas Petlund wrote:
> On 02/18/2010 09:41 AM, Ilpo Järvinen wrote:
>   
> > On Wed, 17 Feb 2010, David Miller wrote:
> >
> >     
> > > From: Andreas Petlund <apetlund@xxxxxxxxx>
> > > Date: Tue, 16 Feb 2010 15:40:41 +0100
> > >
> > >       
> > > > @@ -341,6 +342,8 @@ struct tcp_sock {
> > > >  	u16	advmss;		/* Advertised MSS			*/
> > > >  	u8	frto_counter;	/* Number of new acks after RTO */
> > > >  	u8	nonagle;	/* Disable Nagle algorithm?             */
> > > > +	u8      thin_lto    : 1,/* Use linear timeouts for thin streams */
> > > > +		thin_undef  : 7;
> > > >  
> > > >         
> > > There is now a gap of 3 unused bytes here in this critical
> > > core TCP socket data structure.
> > >
> > > Please either find a way to avoid this hole, or document
> > > it with a comment.
> > >       
> > There would be multiple bits free for use in both frto_counter and nonagle 
> > byte.
> >
> >     
>
> I was playing aroud with this setup:
>
> =========
> u8	nonagle     : 4,/* Disable Nagle algorithm?             */
> 	thin_lto    : 1,/* Use linear timeouts for thin streams */
> 	thin_dupack : 1,/* Fast retransmit on first dupack      */
> 	thin_undef  : 2;
> =========
>
> Do you think that would do the trick?
>   

According to Ilpo, it would be ok to reduce both ftro_counter and
nonagle, so why not join all these into u16 and leave the remaining
free bits documented for other people. Like this:

   u16 frto_counter:x; /* Number of new acks after RTO */
   u16 nonagle:y; /* Disable Nagle algorithm? */
   u16 thin_lto:1; /* Use linear timeouts for thin streams */
   u16 unused:15-x-y;

Not sure about the y and x. Ilpo, can you comment on those values?


Thanks,
Franco
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