From owner-freebsd-virtualization@freebsd.org Sat Oct 14 17:12:44 2017 Return-Path: Delivered-To: freebsd-virtualization@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id BF6DEE27D3E for ; Sat, 14 Oct 2017 17:12:44 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from kenobi.freebsd.org (kenobi.freebsd.org [IPv6:2001:1900:2254:206a::16:76]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id AD62176038 for ; Sat, 14 Oct 2017 17:12:44 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from bugs.freebsd.org ([127.0.1.118]) by kenobi.freebsd.org (8.15.2/8.15.2) with ESMTP id v9EHCiTg094280 for ; Sat, 14 Oct 2017 17:12:44 GMT (envelope-from bugzilla-noreply@freebsd.org) 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!" Date: Sat, 14 Oct 2017 17:12:44 +0000 X-Bugzilla-Reason: AssignedTo X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: Base System X-Bugzilla-Component: kern X-Bugzilla-Version: 11.1-RELEASE X-Bugzilla-Keywords: X-Bugzilla-Severity: Affects Only Me X-Bugzilla-Who: grehan@FreeBSD.org X-Bugzilla-Status: New X-Bugzilla-Resolution: X-Bugzilla-Priority: --- X-Bugzilla-Assigned-To: freebsd-virtualization@FreeBSD.org X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: https://bugs.freebsd.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: freebsd-virtualization@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: "Discussion of various virtualization techniques FreeBSD supports." List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 14 Oct 2017 17:12:44 -0000 https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D222916 --- Comment #6 from Peter Grehan --- >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.=