RE: [Xen-devel] [PATCH] libxl: use named options for tsc_mode

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

> From: Ian Campbell [mailto:ian.campbell@xxxxxxxxxx]
> Subject: [Xen-devel] [PATCH] libxl: use named options for tsc_mode
> 
> # HG changeset patch
> # User Ian Campbell <ian.campbell@xxxxxxxxxx>
> # Date 1320922479 0
> # Node ID bc79b560aafa1e4dc42af00e6a326dc651b5636a
> # Parent  460b507e15f864dd6712f5040e36538d6e076ae4
> libxl: use named options for tsc_mode.
> 
> It seems that this knob is expoerted from the hypervisor as a raw
> integer (no symbolic names) documented in xen/include/asm-x86. Propagating 
> that
> all the way to the end user is hardly friendly (it's bad enough in the
> hypercall interface).

Thanks for looking at this!

> Add an enum at the libxl level with a hopefully descriptive set of names.
> Deprecate the use of an integer in xl cfg files.

We (Oracle) already have shipped cfg files that use the integer
so would prefer that the deprecation message be removed.  IMHO, to
the vast majority of users, the symbolic names will be gibberish
anyway and are likely to be misspelled.  For knowledgeable folk,
they are nice though, so maybe just support both?
 
> +   * `"always_emulate"`: guest rdtsc/p always emulated at 1GHz (kernel
> +     and user).

Many guests will "appear" to run at a slower "bogomips" so a word
or two more here may keep some from panicking.  Maybe:

guest rdtsc/p always emulated and the virtual TSC will appear to
increment (kernel and user) at a fixed 1GHz rate, regardless of
the PCPU HZ rate or power state; this will NOT affect underlying
CPU performance

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