Date: Sat, 14 Oct 2017 17:12:44 +0000 From: bugzilla-noreply@freebsd.org To: freebsd-virtualization@FreeBSD.org Subject: [Bug 222916] [bhyve] Debian guest kernel panics with message "CPU#0 stuck for Xs!" Message-ID: <bug-222916-27103-YmQj5Rlg7I@https.bugs.freebsd.org/bugzilla/> In-Reply-To: <bug-222916-27103@https.bugs.freebsd.org/bugzilla/> References: <bug-222916-27103@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D222916 --- Comment #6 from Peter Grehan <grehan@FreeBSD.org> --- >Or does the interaction between bhyve and the host scheduler somehow >result in the virtual cpus being set aside Yes, though: > for tens of seconds? The error message from Linux is a bit misleading. There is a low-priority kernel thread that tries to run every 5 seconds and then sleeps. If it hasn= 't been able to run for an extended amount of time, for example due to high interrupt activity, higher priority threads running, or spinlocks being hel= d, the error message will be displayed. What I believe you are seeing is a classic hypervisor problem, not specifi= c to bhyve, known as "lock-holder preemption" where a vCPU holding a spin-lock is preempted by the host, and other vCPUs that are running then spin attemptin= g to acquire that lock which can't be released. A search will show the large amo= unt of literature on this issue :) Maybe the best reading on this is the ESXi scheduler paper: =20=20=20 http://www.vmware.com/content/dam/digitalmarketing/vmware/en/pdf/techpaper/= vmware-vsphere-cpu-sched-performance-white-paper.pdf There has been some talk of putting knowledge of vCPUs in the FreeBSD scheduler to allow some form of gang scheduling, but nothing has come of th= at so far. As to your point; it's more than just fairness that the hypervisor schedul= er has to provide - heuristics about guest o/s behaviour are also needed. --=20 You are receiving this mail because: You are the assignee for the bug.=
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