Bug 1547854

Summary:	Latest rt56 real time kernel on Intel i9 has broken TSC
Product:	Red Hat Enterprise MRG	Reporter:	Kazu Yoshida <kyoshida>
Component:	realtime-kernel	Assignee:	Daniel Bristot de Oliveira <daolivei>
Status:	CLOSED ERRATA	QA Contact:	Jiri Kastner <jkastner>
Severity:	high	Docs Contact:	Petr Bokoc <pbokoc>
Priority:	high
Version:	2.5	CC:	bhu, daolivei, lgoncalv, mgaykar, pbokoc, prarit, williams
Target Milestone:	2.5
Target Release:	---
Hardware:	x86_64
OS:	Linux
Whiteboard:
Fixed In Version:	kernel-rt-3.10.0-693.24.1.rt56.609.el6rt	Doc Type:	Bug Fix
Doc Text:	Intel Core X-Series (Skylake) processors use a hardcoded Time Stamp Counter (TSC) frequency of 25 MHz. In some cases this can be imprecise and lead to timing-related problems such as time drift, timers being triggered early, or TSC clock instability. This update mitigates these problems by no longer using the "native_calibrate_tsc()" function to define the TSC frequency. Refined calibration is now used to update the clock rate accordingly in these cases.	Story Points:	---
Clone Of:		Environment:
Last Closed:	2018-04-17 15:34:33 UTC	Type:	Bug
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description Kazu Yoshida 2018-02-22 06:27:27 UTC

Description of problem:

Latest rt56 real time kernel on Intel i9 has broken TSC

Feb 20 06:55:24 uk01ds300 kernel: tsc: Detected 2600.000 MHz processor
Feb 20 06:55:24 uk01ds300 kernel: TSC synchronization [CPU#0 -> CPU#1]:
Feb 20 06:55:24 uk01ds300 kernel: Measured 115899160216746 cycles TSC warp between CPUs, turning off TSC clock.
Feb 20 06:55:24 uk01ds300 kernel: tsc: Marking TSC unstable due to check_tsc_sync_source failed


Version-Release number of selected component (if applicable):

Red Hat Enterprise MRG Realtime 2.5
3.10.0-693.17.1.rt56.604.el6rt.x86_64 

CPU: 
model name      : Intel(R) Core(TM) i9-7980XE CPU @ 2.60GHz

X299 chipset 


How reproducible:

100% at every boot


Steps to Reproduce:
1. Boot into 3.10.0-693.17.1.rt56.604.el6rt.x86_64


Actual results:

TSC clock turns off.


Expected results:

TSC clock to work correctly.


Additional info:

The issue seems to be fixed in upstream.

https://patchwork.kernel.org/patch/10177655/

https://patchwork.kernel.org/patch/10128789/
https://patchwork.kernel.org/patch/10128793/
https://patchwork.kernel.org/patch/10128791/

Comment 23 Daniel Bristot de Oliveira 2018-04-13 13:17:56 UTC

Hi Petr,

It is ok, Thanks!

-- Daniel

Comment 25 errata-xmlrpc 2018-04-17 15:34:33 UTC

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHSA-2018:1170