Two things: do you get the same results when the client is directly on the Varnish server? (ie. not going through the switch) And is each new request opening a new connection?
-- Guillaume Quintard On Thu, Jul 6, 2017 at 6:45 AM, Andrei <[email protected]> wrote: > Out of curiosity, what does ethtool show for the related nics on both > servers? I also have Varnish on a 10G server, and can reach around > 7.7Gbit/s serving anywhere between 6-28k requests/second, however it did > take some sysctl tuning and the westwood TCP congestion control algo > > On Wed, Jul 5, 2017 at 3:09 PM, John Salmon <John.Salmon@deshawresearch. > com> wrote: > >> I've been using Varnish in an "intranet" application. The picture is >> roughly: >> >> origin <-> Varnish <-- 10G channel ---> switch <-- 1G channel --> client >> >> The machine running Varnish is a high-performance server. It can >> easily saturate a 10Gbit channel. The machine running the client is a >> more modest desktop workstation, but it's fully capable of saturating >> a 1Gbit channel. >> >> The client makes HTTP requests for objects of size 128kB. >> >> When the client makes those requests serially, "useful" data is >> transferred at about 80% of the channel bandwidth of the Gigabit >> link, which seems perfectly reasonable. >> >> But when the client makes the requests in parallel (typically >> 4-at-a-time, but it can vary), *total* throughput drops to about 25% >> of the channel bandwidth, i.e., about 30Mbyte/sec. >> >> After looking at traces and doing a fair amount of experimentation, we >> have reached the tentative conclusion that we're seeing "TCP Incast >> Throughput Collapse" (see references below) >> >> The literature on "TCP Incast Throughput Collapse" typically describes >> scenarios where a large number of servers overwhelm a single inbound >> port. I haven't found any discussion of incast collapse with only one >> server, but it seems like a natural consequence of a 10Gigabit-capable >> server feeding a 1-Gigabit downlink. >> >> Has anybody else seen anything similar? With Varnish or other single >> servers on 10Gbit to 1Gbit links. >> >> The literature offers a variety of mitigation strategies, but there are >> non-trivial tradeoffs and none appears to be a silver bullet. >> >> If anyone has seen TCP Incast Collapse with Varnish, were you able to work >> around it, and if so, how? >> >> Thanks, >> John Salmon >> >> References: >> >> http://www.pdl.cmu.edu/Incast/ >> >> Annotated Bibliography in: >> https://lists.freebsd.org/pipermail/freebsd-net/2015-Novembe >> r/043926.html >> >> -- >> *.* >> >> _______________________________________________ >> varnish-misc mailing list >> [email protected] >> https://www.varnish-cache.org/lists/mailman/listinfo/varnish-misc >> > > > _______________________________________________ > varnish-misc mailing list > [email protected] > https://www.varnish-cache.org/lists/mailman/listinfo/varnish-misc >
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