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From: "Radim Krčmář" <rkrcmar@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: David Hildenbrand <david@redhat.com>,
	Don Bowman <db@donbowman.ca>,
	kvm@vger.kernel.org
Subject: Re: PATCH: setup_vmcs_config: disable TSC scaling on unlike processors
Date: Tue, 6 Dec 2016 12:08:58 +0100	[thread overview]
Message-ID: <20161206110858.GC8660@potion> (raw)
In-Reply-To: <f522b8f6-aea5-2fcd-575f-72272013173e@redhat.com>

2016-12-06 10:09+0100, Paolo Bonzini:
> On 06/12/2016 09:49, David Hildenbrand wrote:
>>>>
>>>> I feel a better solution is to mask off this capability on the one
>>>> processor.
>>>
>>> I like the global toggle better -- it is less code with more uses.
>> 
>> (not having much insight) what speaks against allowing such features
>> only if available on all CPUs symmetrically? I actually prefer having an
>> automatism to some magic toggle.
> 
> I agree with David.  Just warn and proceed with the minimum common set
> of features.

Yes, that is reasonable -- I though David wanted to use the feature when
running on CPUs that support it (only mask off on the one).

I'd start with changing the check in vmx_check_processor_compat() to
ignore disabled features and then extend KVM to enable only the common
set.

Finding the minimal set of common features is complicated by hotplug ...
I think that the check we have is not working perfectly, so if you
currently

 1) offline all cores on the worse CPU
 2) load kvm module
 3) online all CPUs

then KVM is going enable tsc-scaling and not complain, but guests
running on onlined CPUs are not going to work.
Can you confirm that?

Thanks.

  reply	other threads:[~2016-12-06 11:09 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-12-02  2:32 PATCH: setup_vmcs_config: disable TSC scaling on unlike processors Don Bowman
2016-12-02 15:07 ` Radim Krčmář
2016-12-02 19:10   ` Don Bowman
2016-12-02 20:58     ` Don Bowman
2016-12-05 16:37       ` Radim Krčmář
2016-12-06  8:49   ` David Hildenbrand
2016-12-06  9:09     ` Paolo Bonzini
2016-12-06 11:08       ` Radim Krčmář [this message]
2016-12-07 11:37         ` David Hildenbrand
2016-12-07 15:25           ` Radim Krčmář
2016-12-08 11:46             ` David Hildenbrand
2016-12-08 14:32               ` Radim Krčmář
2016-12-09 15:12                 ` Don Bowman
2016-12-13 15:43                   ` Radim Krčmář
2016-12-14  4:07                     ` Don Bowman
2016-12-14 12:30                       ` Paolo Bonzini
2016-12-14 12:46                     ` Paolo Bonzini

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