Re: [Qemu-devel] [PATCH v3 0/2] Allow migration with invtsc if TSC frequency is explicitly set

[Marcelo Tosatti]

On Sun, Jan 08, 2017 at 03:32:32PM -0200, Eduardo Habkost wrote:
> This series makes QEMU accept migration if tsc-frequency is
> explicitly set on configuration. As management software is
> required to keep device configuration the same on migration
> source or destination, explicit tsc-frequency will ensure that
> either:
> 
> * The destination host has a matching TSC frequency; or
> * The destination host has TSC scaling available.
> 
> Changelog
> =========
> 
> v2 -> v3:
> * Fix build failure ((missing closing braces)
> 
> v1 -> v2:
> * v1 series subject was:
>   * [PATCH 0/4] Allow migration with invtsc if there's no
>     frequency mismatch
> * Removed patches 3/4 and 4/4, that allowed migration
>   if no explicit tsc-frequency was set. Implementing the check on
>   post_load or post_init is not enough to make migration abort,
>   so we will need a more complex solution to implement that
>   feature.
> 
> Plans for future work
> =====================
> 
> 1) Querying host TSC frequency/scaling capability
> -------------------------------------------------
> 
> I plan to include TSC frequency/scaling information on
> query-cpu-model-expansion model="host" in a future series. Then
> management software will be able to automatically configure TSC
> frequency when invtsc is enabled, instead of requiring the user
> to configure it explicitly. While we don't implement that, invtsc
> migration will be possible only if the user configures TSC
> frequency manually.
> 
> 2) invtsc migration with no explicit TSC frequency
> --------------------------------------------------
> 
> A future series can implement migration when TSC frequency is not
> specified explicitly. It will be a bit more complex because it
> requires either letting the destination abort the migration, or
> sending TSC frequency/scaling information from destination to
> source.
> 
> ---
> Cc: Marcelo Tosatti <address@hidden>
> Cc: "Daniel P. Berrange" <address@hidden>
> Cc: Paolo Bonzini <address@hidden>
> Cc: address@hidden
> Cc: Haozhong Zhang <address@hidden>
> Cc: "Michael S. Tsirkin" <address@hidden>
> Cc: Igor Mammedov <address@hidden>
> Cc: address@hidden
> Cc: Jiri Denemark <address@hidden>
> 
> Eduardo Habkost (2):
>   kvm: Simplify invtsc check
>   kvm: Allow invtsc migration if tsc-khz is set explicitly
> 
>  target/i386/kvm.c | 20 +++++++++++---------
>  1 file changed, 11 insertions(+), 9 deletions(-)
> 
> -- 
> 2.11.0.259.g40922b1

Looks good to me.