Bug 870484 - cpu 'host-model' should support features in force or disable mode
cpu 'host-model' should support features in force or disable mode
Product: Red Hat Enterprise Linux 6
Classification: Red Hat
Component: libvirt (Show other bugs)
Unspecified Unspecified
unspecified Severity unspecified
: rc
: ---
Assigned To: Peter Krempa
Virtualization Bugs
: Upstream
Depends On: 799354
Blocks: 865505 956468 1059007
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Reported: 2012-10-26 11:40 EDT by Dave Allan
Modified: 2016-04-26 11:28 EDT (History)
11 users (show)

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Fixed In Version:
Doc Type: Bug Fix
Doc Text:
Story Points: ---
Clone Of: 799354
: 956468 (view as bug list)
Last Closed: 2014-04-04 17:00:13 EDT
Type: ---
Regression: ---
Mount Type: ---
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Verified Versions:
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oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

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Description Dave Allan 2012-10-26 11:40:16 EDT
+++ This bug was initially created as a clone of Bug #799354 +++

Would be handy to have <cpu mode='host-model'> support <feature policy='force'/> or policy=disable. That way tools have an option to turn on x2apic for kvm guests which provides a performance boost with no downsides, but doesn't require host CPU support.

--- Additional comment from rjones@redhat.com on 2012-10-25 14:05:16 EDT ---

Also <feature policy='disable'/>.  For one use case, see:
Comment 1 Jiri Denemark 2012-10-29 09:13:31 EDT
I'm the owner of upstream brother of this bug.
Comment 2 Andrew Cathrow 2012-12-31 17:11:37 EST
Depending on the implementation of this we may want to close 891015 which covers host passthrough mode.
Comment 3 Peter Krempa 2013-07-16 05:14:32 EDT
Fixed upstream with:

commit 3c8be55c04eb2647fd5c9d51efae78f7afdcec85
Author: Peter Krempa <pkrempa@redhat.com>
Date:   Mon Jul 15 17:38:55 2013 +0200

    cpu: Allow fine tuning of "host-model" cpu
    Until now, the "host-model" cpu mode couldn't be influenced. This patch
    allows to use the <feature> elements to either enable or disable
    specific CPU flags. This can be used to force flags that can be emulated
    even if the host CPU doesn't support them.

commit 13cdd389ed06e81277f208c269d825046cdbb4cb
Author: Peter Krempa <pkrempa@redhat.com>
Date:   Mon Jul 15 14:36:09 2013 +0200

    cpu: Add virCPUDefUpdateFeature()
    This new function updates or adds a feature to a existing cpu model
    definition. This function will be helpful to allow tuning of
    "host-model" features in later patches.

Comment 5 Jiri Denemark 2013-07-31 07:07:57 EDT
This bug has already been fixed upstream but it is considered
unsuitable for backporting to RHEL 6.5 because at least one of the
following conditions is met:

- the patches required to address this bug are complex or invasive
  causing the backport to be too risky
- this bug is not important enough to justify backporting non-trivial
  patches for it

Thus I'm pushing this bug to RHEL 6.6 (and setting Upstream keyword to
indicate we have patches upstream) for now. If you don't agree with
this resolution, please, give us reasons which you think are strong
enough for us to reevaluate the decision not to backport patches for
this bug.
Comment 7 RHEL Product and Program Management 2014-04-04 17:00:13 EDT
Development Management has reviewed and declined this request.
You may appeal this decision by reopening this request.

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