tcpcb cleanup?

[Randall Stewart]

Yes

As I said in comments to your removal of the sack field, they have
drifted since my first work.

I am not too concerned since the first 3 cache lines are the most used and most
important.

I do intend to do a re-analysis once I get BBR and the latest Rack in to see if
we could improve things.. though it is doubtful that we will gain much (but you never know) ;)

R

> On Jul 29, 2019, at 11:13 PM, Scheffenegger, Richard <Richard.Scheffenegger at netapp.com> wrote:
> 
> Hi,
> 
> I've been looking into the cache line alignment today (because D18811).
> 
> Found that the commented cache lines only align to line 3 - then they drift from the comments.
> 
> For example, t_rttupdated is defined as u_long (8 bytes), while it really only tracks if at least some (small) number of rtt samples were collected, to start the  use of the rtt vars...
> 
> Realistically, a uint8_t with a limited increment (if (x<255) x++) would serve the very same function...
> 
> Other example: t_sndzerowin (in tcpcb) appears to be only a counter, better placed into the tcpstat structure, where non-functional counters belong IMHO. (perhaps a per-session variant).
> 
> 
> 
> 
> And the other variables could probably be defined in the explicit types (uint16/32/64), to be more certain of the alignment - plus making sure that alignment boundaries between different sized types don't result in unintentional shifting of the alignment (like it seems currently to be the case).
> 
> Another prime example: struct sackhint is 40 bytes, only 24 of these are actually used; and ideally, sackblks, snd_fack share the same line, while sackhint and snd_holes would do the same (currently, both are distributed across 2)	....
> 
> 
> Any appetite to get the (higher) cache lines aligned in tcpcb?
> 
> Best regards,
>   Richard
> 
> 
> _______________________________________________
> freebsd-transport at freebsd.org mailing list
> https://lists.freebsd.org/mailman/listinfo/freebsd-transport
> To unsubscribe, send any mail to "freebsd-transport-unsubscribe at freebsd.org"

------
Randall Stewart
rrs at netflix.com