svn commit: r295136 - in head: sys/kern sys/netinet sys/sys usr.bin/netstat

[Slawa Olhovchenkov]

On Tue, Feb 02, 2016 at 01:21:52PM -0800, Alfred Perlstein wrote:

> >>> I would second John's comment on the necessity of the change though,
> >>> if one already have 32K of *backlogged* connections, it's probably not
> >>> very useful to allow more coming in.  It sounds like the application
> >>> itself is seriously broken, and unless expanding the field have some
> >>> performance benefit, I don't think it should stay.
> >> Imagine a hugely busy image board like 2ch.net, if there is a single
> >> hiccup, it's very possible to start dropping connections.
> > In reality start dropping connections in any case: nobody will be
> > infinity wait of accept (user close browser and go away, etc).
> >
> > Also, if you have more then 4K backloged connections -- you have
> > problem, you can't process all connections request and in next second
> > you will be have 8K, after next second -- 12K and etc.
> >


> In our case the user would not really know if our "page" didn't load 
> because we were just an invisible gif.
> 
> So back to the example, let's scale that out to today's numbers.
> 
> 100mbps -> 10gigE, so that would be 1500 conn/sec -> 150,000 conn/sec.  
> so basically at 0.20 of a second of any sort of latency I will be 
> overflowing the listen queue and dropping connections.

OK, you talk about very specilal case -- extremaly short connections,
about one data packet. Yes, in this case you got this behaivor.
I think case of 2ch is different.

> Now when you still have CPU to spare because connections *are* precious, 
> then the model makes sense to slightly over-provision the servers to 
> allow for somebacklog to be processed.
> 
> So, in today's day and age, it really does make sense to allow for 
> buffering more than 32k connections, particularly if the developer knows 
> what he is doing.
> 
> Does this help explain the reasoning?

Yes, some special cases may be exist.