Date: Wed, 3 Feb 2016 00:41:12 +0300 From: Slawa Olhovchenkov <slw@zxy.spb.ru> To: Alfred Perlstein <alfred@freebsd.org> Cc: Xin LI <delphij@gmail.com>, "svn-src-head@freebsd.org" <svn-src-head@freebsd.org>, "svn-src-all@freebsd.org" <svn-src-all@freebsd.org>, "src-committers@freebsd.org" <src-committers@freebsd.org>, John Baldwin <jhb@freebsd.org> Subject: Re: svn commit: r295136 - in head: sys/kern sys/netinet sys/sys usr.bin/netstat Message-ID: <20160202214112.GR88527@zxy.spb.ru> In-Reply-To: <56B11DF0.3060401@freebsd.org> References: <201602020557.u125vxCP084718@repo.freebsd.org> <36439709.poT7RgRunK@ralph.baldwin.cx> <56B10D67.4050602@freebsd.org> <CAGMYy3v4s-UQpO3-oq8B1V1NvzyGSmJU49zDUL9oPy21sYkWCQ@mail.gmail.com> <56B11323.70905@freebsd.org> <20160202210958.GV37895@zxy.spb.ru> <56B11DF0.3060401@freebsd.org>
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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.
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