My understanding is that idle=nomwait disables the use of the MWAIT instruction in the kernel implementation of the CPU idle state.
I also *think* that, under the hood, disabling C6 and the "Typical Power idle" option also have a similar (or perhaps the same?) effect of reducing the use of MWAIT. E.g., since I started enabling the "Typical Power idle" option in my BIOS, at every boot I have the following message showing up in the kernel logs: [Firmware Bug]: ACPI MWAIT C-state 0x0 not supported by HW (0x0) However, because the MWAIT instruction is part of SSE3 [1], it might end up being executed by any software which was compiled with support for SSE3. So I believe that disabling MWAIT for idle states greatly reduces the risk of getting these MWAIT hangs (simply because the instruction will end up being executed much less), but it will not completely eliminate them. Thus, it seems like the only bulletproof solution is either to upgrade to Ryzen+/Ryzen2, or to disable hypterthreading. [1] https://en.wikipedia.org/wiki/SSE3 -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. https://bugs.launchpad.net/bugs/1690085 Title: Ryzen 1800X freeze - rcu_sched detected stalls on CPUs/tasks Status in Linux: Confirmed Status in linux package in Ubuntu: Confirmed Bug description: Hi, We aregetting various kernel crash on a pretty new config. We're using Ryzen 1800X CPU with X370 Gaming Pro Carbon MB (7A32V1) using latest BIOS available (1.52) We are running Ubuntu 17.04 (amd64), we've tried different kernel version, native one and releases from http://kernel.ubuntu.com/~kernel-ppa/mainline/ too. Tested kernel version: native 17.04 kernel 4.10.15 Issues are the same, we're getting random freeze on the machine. Here is kern.log entry when happening : May 10 22:41:56 dev2 kernel: [24366.186246] INFO: rcu_sched detected stalls on CPUs/tasks: May 10 22:41:56 dev2 kernel: [24366.187618] 0-...: (1 GPs behind) idle=49b/1/0 softirq=28561/28563 fqs=913449 May 10 22:41:56 dev2 kernel: [24366.188977] (detected by 12, t=1860207 jiffies, g=10001, c=10000, q=4656) May 10 22:41:56 dev2 kernel: [24366.190344] Task dump for CPU 0: May 10 22:41:56 dev2 kernel: [24366.190345] swapper/0 R running task 0 0 0 0x00000008 May 10 22:41:56 dev2 kernel: [24366.190348] Call Trace: May 10 22:41:56 dev2 kernel: [24366.190354] ? native_safe_halt+0x6/0x10 May 10 22:41:56 dev2 kernel: [24366.190355] ? default_idle+0x20/0xd0 May 10 22:41:56 dev2 kernel: [24366.190358] ? arch_cpu_idle+0xf/0x20 May 10 22:41:56 dev2 kernel: [24366.190360] ? default_idle_call+0x23/0x30 May 10 22:41:56 dev2 kernel: [24366.190362] ? do_idle+0x16f/0x200 May 10 22:41:56 dev2 kernel: [24366.190364] ? cpu_startup_entry+0x71/0x80 May 10 22:41:56 dev2 kernel: [24366.190366] ? rest_init+0x77/0x80 May 10 22:41:56 dev2 kernel: [24366.190368] ? start_kernel+0x464/0x485 May 10 22:41:56 dev2 kernel: [24366.190369] ? early_idt_handler_array+0x120/0x120 May 10 22:41:56 dev2 kernel: [24366.190371] ? x86_64_start_reservations+0x24/0x26 May 10 22:41:56 dev2 kernel: [24366.190372] ? x86_64_start_kernel+0x14d/0x170 May 10 22:41:56 dev2 kernel: [24366.190373] ? start_cpu+0x14/0x14 May 10 22:44:56 dev2 kernel: [24546.188093] INFO: rcu_sched detected stalls on CPUs/tasks: May 10 22:44:56 dev2 kernel: [24546.189461] 0-...: (1 GPs behind) idle=49b/1/0 softirq=28561/28563 fqs=935027 May 10 22:44:56 dev2 kernel: [24546.190823] (detected by 14, t=1905212 jiffies, g=10001, c=10000, q=4740) May 10 22:44:56 dev2 kernel: [24546.192191] Task dump for CPU 0: May 10 22:44:56 dev2 kernel: [24546.192192] swapper/0 R running task 0 0 0 0x00000008 May 10 22:44:56 dev2 kernel: [24546.192195] Call Trace: May 10 22:44:56 dev2 kernel: [24546.192199] ? native_safe_halt+0x6/0x10 May 10 22:44:56 dev2 kernel: [24546.192201] ? default_idle+0x20/0xd0 May 10 22:44:56 dev2 kernel: [24546.192203] ? arch_cpu_idle+0xf/0x20 May 10 22:44:56 dev2 kernel: [24546.192204] ? default_idle_call+0x23/0x30 May 10 22:44:56 dev2 kernel: [24546.192206] ? do_idle+0x16f/0x200 May 10 22:44:56 dev2 kernel: [24546.192208] ? cpu_startup_entry+0x71/0x80 May 10 22:44:56 dev2 kernel: [24546.192210] ? rest_init+0x77/0x80 May 10 22:44:56 dev2 kernel: [24546.192211] ? start_kernel+0x464/0x485 May 10 22:44:56 dev2 kernel: [24546.192213] ? early_idt_handler_array+0x120/0x120 May 10 22:44:56 dev2 kernel: [24546.192214] ? x86_64_start_reservations+0x24/0x26 May 10 22:44:56 dev2 kernel: [24546.192215] ? x86_64_start_kernel+0x14d/0x170 May 10 22:44:56 dev2 kernel: [24546.192217] ? start_cpu+0x14/0x14 Depending on the kernel version, we've got NMI watchdog errors related to CPU stuck (mentioning the CPU core id, which is random). Crash is happening randomly, but in general after some hours (3-4h). Now, we've installed kernel 4.11.0-041100-generic #201705041534 this morning and waiting for crash... For now, the machine is not "used", at least, it's not CPU stressed... Thanks --- ApportVersion: 2.20.4-0ubuntu4 Architecture: amd64 DistroRelease: Ubuntu 17.04 InstallationDate: Installed on 2017-05-09 (1 days ago) InstallationMedia: Ubuntu-Server 17.04 "Zesty Zapus" - Release amd64 (20170412) Package: linux (not installed) ProcEnviron: TERM=xterm-256color PATH=(custom, no user) XDG_RUNTIME_DIR=<set> LANG=fr_FR.UTF-8 SHELL=/bin/bash Tags: zesty Uname: Linux 4.11.0-041100-generic x86_64 UnreportableReason: The running kernel is not an Ubuntu kernel UpgradeStatus: No upgrade log present (probably fresh install) UserGroups: _MarkForUpload: True To manage notifications about this bug go to: https://bugs.launchpad.net/linux/+bug/1690085/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
