linux-kernel - Re: [PATCH ] Documentation/kvm: Update cpuid documentation for steal time and pv eoi

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Message-ID: <20130826070703.GB23859@redhat.com>
Date:	Mon, 26 Aug 2013 10:07:03 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
Cc:	Gleb Natapov <gleb@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Rob Landley <rob@...dley.net>, mtosatti@...hat.com
Subject: Re: [PATCH ] Documentation/kvm: Update cpuid documentation for steal
 time and pv eoi

On Fri, Aug 23, 2013 at 05:34:47PM +0530, Raghavendra K T wrote:
> Signed-off-by: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
> ---
>  While adding documentation for pvspinlock, I found that these two should
>  be updated. I have based this on top of pvspinlock kvm host patchset (V12)

I would change the description to merely say what the CPUID bits
mean, and what they mean is exactly that an MSR is valid.
Use KVM_FEATURE_ASYNC_PF as a template.


>  Documentation/virtual/kvm/cpuid.txt | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt
> index 22ff659..15a5ac20 100644
> --- a/Documentation/virtual/kvm/cpuid.txt
> +++ b/Documentation/virtual/kvm/cpuid.txt
> @@ -43,6 +43,15 @@ KVM_FEATURE_CLOCKSOURCE2           ||     3 || kvmclock available at msrs
>  KVM_FEATURE_ASYNC_PF               ||     4 || async pf can be enabled by
>                                     ||       || writing to msr 0x4b564d02
>  ------------------------------------------------------------------------------
> +KVM_FEATURE_STEAL_TIME             ||     5 || guest accounts fine granularity
> +                                   ||       || task steal time.

I'm not sure what this phrase means.
Steal time is a host feature, not a guest feature:
IIUC if this bit is set, the hypervisor can pass the guest information
about how much time was spent running other processes outside the VM.

> enabled when
> +                                   ||       || shedstat or task delay accounting
> +                                   ||       || is supported by the host.

I think it's enabled by guest, not by host.


> +------------------------------------------------------------------------------
> +KVM_FEATURE_PV_EOI                 ||     6 || overrides the generic EOI
> +                                   ||       || implementation with an optimized
> +                                   ||       || version.

More exactly "with a paravirtualized version".

> +------------------------------------------------------------------------------
>  KVM_FEATURE_PV_UNHALT              ||     7 || guest checks this feature bit
>                                     ||       || before enabling paravirtualized
>                                     ||       || spinlock support.
> -- 
> 1.7.11.7
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