Date: Thu, 21 Jan 2016 16:56:57 -0500 From: Ryan Stone <rysto32@gmail.com> To: freebsd-transport@freebsd.org Subject: Flamegraph of 8KB message bottlenecks Message-ID: <CAFMmRNzBfNB7Fr3VYKJwHpxt1CBc4gT6Yh%2Bqx2u2O_K1KF3nxQ@mail.gmail.com>
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I brought up on the -transport call last week that I was having trouble receiving 8KB packets at 40Gbps. I blamed "TCP stack" peformance, although what I really meant was "kernel performance" -- I just assumed that the problem was in the stack. From looking at a flamegraph, I'm not so sure this was the case. The flamegraph was taken on a "FreeBSD 10.1-ish" system. Unfortunately running stock FreeBSD head in this environment is quite difficult, so I probably wouldn't be able to check if anything on head has alleviated things. You can see the flamegraph for youself here: https://people.freebsd.org/~rstone/incast_8kb_flame.svg You'll note that my underland application is way off in the bottom left, taking 3% of all cycles. Meanwhile top reports that the system is completely bogged down in interrupt and system time.
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