Bug 728551

Summary:	add /sys/kernel/realtime entry
Product:	Red Hat Enterprise MRG	Reporter:	Luis Claudio R. Goncalves <lgoncalv>
Component:	realtime-kernel	Assignee:	Luis Claudio R. Goncalves <lgoncalv>
Status:	CLOSED ERRATA	QA Contact:	Jiri Kastner <jkastner>
Severity:	low	Docs Contact:
Priority:	medium
Version:	1.1	CC:	bhu, jkastner, lgoncalv
Target Milestone:	2.0.8
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
Whiteboard:
Fixed In Version:		Doc Type:	Bug Fix
Doc Text:	Cause: the old method used to assert if the running kernel is realtime enabled or not depended on parsing the output of 'uname -v'. Consequence: That process, when repeated multiple times could become costly and a source of latencies. Fix: add a file, created only when the kernel is reatime enabled, in /sys, that is an in-memory filesystem and is cheaper to read. Result: It is ten times faster to verify if the kernel has RT capabilities or not.	Story Points:	---
Clone Of:		Environment:
Last Closed:	2011-09-12 19:48:00 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description Luis Claudio R. Goncalves 2011-08-05 14:22:23 UTC

Add a /sys/kernel entry to indicate that the kernel is a realtime kernel.

This makes it easier (and faster and cheaper) to determine if you're
running on an RT kernel than parsing the output of uname -v.

We found this when we had a udev rule for detecting IRQ registration
that looked at the output of uname -v, looking for the ' RT ' string.
This rule prevented a 32-core box from booting (or delayed it past the
point we were willing to wait) because it was invoking the rule
repeatedly for each core being brought up.

Comment 1 Luis Claudio R. Goncalves 2011-08-05 14:38:54 UTC

The following commit has been queued for the Errata:

    2e76e55 add /sys/kernel/realtime entry

Comment 5 Luis Claudio R. Goncalves 2011-08-29 16:24:02 UTC

    Technical note added. If any revisions are required, please edit the "Technical Notes" field
    accordingly. All revisions will be proofread by the Engineering Content Services team.
    
    New Contents:
Cause: the old method used to assert if the running kernel is realtime enabled or not depended on parsing the output of 'uname -v'.
Consequence: That process, when repeated multiple times could become costly and a source of latencies.
Fix: add a file, created only when the kernel is reatime enabled, in /sys, that is an in-memory filesystem and is cheaper to read.
Result: It is ten times faster to verify if the kernel has RT capabilities or not.

Comment 6 errata-xmlrpc 2011-09-12 19:48:00 UTC

An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on therefore solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.

http://rhn.redhat.com/errata/RHSA-2011-1253.html