Date: Tue, 24 Jul 2018 15:30:32 -0600 From: Alan Somers <asomers@freebsd.org> To: "freebsd-virtualization@freebsd.org" <virtualization@freebsd.org> Subject: Overcommitting CPUs with BHyve? Message-ID: <CAOtMX2hEPnBaaKk25YWe6mYW-gCA6pGssEHTBB4GJ-C6sQU%2Btg@mail.gmail.com>
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What are people's experiences with overcommitting CPUs in BHyve? I have an 8-core machine that often runs VMs totalling up to 5 allocated CPUs without problems. But today I got greedy. I assigned 8 cores to one VM for a big build job. Obviously, some of those were shared with the host. I also assigned it 8GB of RAM (out of 16 total). Build performance fell through the floor, even though the host was idle. Eventually I killed the build and restarted it with a more modest 2 make jobs (but the VM still had 8 cores). Performance improved. But eventually the system seemed to be mostly hung, while I had a build job running on the host as well as in the VM. I killed both build jobs, which resolved the hung processes. Then I restarted the host's build alone, and my system completely hung, with top(1) indicating that many processes were in the pfault state. So my questions are: 1) Is it a known problem to overcommit CPUs with BHyve? 2) Could this be related to the pfault hang, even though the guest was idle at the time? -Alan
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