apport information ** Attachment added: "Lspci.txt" https://bugs.launchpad.net/bugs/1564949/+attachment/4619528/+files/Lspci.txt
-- 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/1564949 Title: Severe latency/skew on AMD Opetron processor Status in linux package in Ubuntu: Confirmed Bug description: Discovered this while doing pre-release certification testing for 16.04 on an HP ProLiant DL385p Gen8 with an AMD Opteron 6320 8-core CPU. I have some code that essentially does this: And note, I am NOT a C programmer, I know enough C to read it and do some minor things, and I once knew C++ fairly well, about 10 years ago... gettimeofday(&tval_start, NULL); sleep(sleeptime); gettimeofday(&tval_stop, NULL); where tval_start and tval_stop are timeval structs and sleeptime is 60. Once it gets the start and stop it finds the delta minus the sleep time. In a perfect world, for example, start time would be 123456.123 and end time would be 123516.123 and the delta between them minus the 60 seconds of sleep would be 0. Of course, that isn't how it works in reality so the delta may be a few microseconds here and there depending on what else the kernel is doing at any given moment. The following, however, are on essentially idle Xenial systems (only processes running are whatever Ubuntu Server runs by default, nothing really taxing going on). On my Skylake i7 with Xenial, the time differences are never more than a few 10,000ths of a second: (kernel 4.4.0-15.31) Testing clock direction for 5 minutes... PASSED: Iteration 0 delta: 0.000109 PASSED: Iteration 1 delta: 0.000068 PASSED: Iteration 2 delta: 0.000107 PASSED: Iteration 3 delta: 0.000216 PASSED: Iteration 4 delta: 0.000089 On a zVM instance (kernel 4.4.0-16.32) it's even better: PASSED: Iteration 0 delta: 0.000058 PASSED: Iteration 1 delta: 0.000058 PASSED: Iteration 2 delta: 0.000074 PASSED: Iteration 3 delta: 0.000052 PASSED: Iteration 4 delta: 0.000062 But on an AMD cpu with Xenial (the only AMD CPU I have access to), the difference is always in the 10ths of a second, sometimes even several seconds... in other words, I've seen up to a 7.9 second delta with this code. Here's one run that shows 3 seconds in one iteration: (kernel 4.4.0-15.31) FAILED: Iteration 0 delta: 3.057980 FAILED: Iteration 1 delta: 0.225712 FAILED: Iteration 2 delta: 0.241468 FAILED: Iteration 3 delta: 0.229084 FAILED: Iteration 4 delta: 0.223933 I ran a second run on the AMD cpu and the latency was all over the place: FAILED: Iteration 0 delta: 9.302149 FAILED: Iteration 1 delta: 0.624466 FAILED: Iteration 2 delta: 1.644834 FAILED: Iteration 3 delta: 1.011474 FAILED: Iteration 4 delta: 0.923033 After a discussion with cking and apw, deviations of as seen on the Intel and s390 CPUs are about what we should expect to see depending on what the system is doing at the moment gettimeofday() is executed. However, on the AMD CPU, differences of up to 9 seconds or more are NOT expected and highly irregular. Colin said he tested this on an AMD C60 CPU and got numbers inline with the Skylake and s390 chips and could not reproduce the times I am seeing on the Opteron. $ cat /proc/version_signature Ubuntu 4.4.0-15.31-generic 4.4.6 --- AlsaDevices: total 0 crw-rw---- 1 root audio 116, 1 Mar 31 17:21 seq crw-rw---- 1 root audio 116, 33 Mar 31 17:21 timer AplayDevices: Error: [Errno 2] No such file or directory ApportVersion: 2.20-0ubuntu3 Architecture: amd64 ArecordDevices: Error: [Errno 2] No such file or directory AudioDevicesInUse: Error: [Errno 2] No such file or directory DistroRelease: Ubuntu 16.04 HibernationDevice: RESUME=UUID=b6a44b05-ebe0-4d1c-a525-69d4748960f8 IwConfig: Error: [Errno 2] No such file or directory MachineType: HP ProLiant DL385p Gen8 Package: linux (not installed) PciMultimedia: ProcEnviron: TERM=xterm PATH=(custom, no user) XDG_RUNTIME_DIR=<set> LANG=en_US.UTF-8 SHELL=/bin/bash ProcFB: ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-4.4.0-15-generic root=UUID=70808172-98ba-4129-a185-20a112bdc4fe ro rootdelay=60 ProcVersionSignature: Ubuntu 4.4.0-15.31-generic 4.4.6 RelatedPackageVersions: linux-restricted-modules-4.4.0-15-generic N/A linux-backports-modules-4.4.0-15-generic N/A linux-firmware 1.157 RfKill: Error: [Errno 2] No such file or directory Tags: xenial uec-images Uname: Linux 4.4.0-15-generic x86_64 UpgradeStatus: No upgrade log present (probably fresh install) UserGroups: adm cdrom dip lpadmin lxd plugdev sambashare sudo _MarkForUpload: True dmi.bios.date: 02/06/2014 dmi.bios.vendor: HP dmi.bios.version: A28 dmi.chassis.type: 23 dmi.chassis.vendor: HP dmi.modalias: dmi:bvnHP:bvrA28:bd02/06/2014:svnHP:pnProLiantDL385pGen8:pvr:cvnHP:ct23:cvr: dmi.product.name: ProLiant DL385p Gen8 dmi.sys.vendor: HP To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1564949/+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
