Re: [Xen-devel] [PATCH for-4.6 2/3] xl: fix vNUMA vcpus parsing

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Wed, 2015-08-12 at 20:36 +0100, Wei Liu wrote:
> Originally, if user didn't specify maxvcpus= in xl config file, the
> maximum size of vcpu bitmap was always equal to maximum number of pcpus.
> This might not be what user wants.

What are you suggesting they wanted instead? We are only talking about the
bitmap right, and the typical/sensible config will have #vcpus <= #pcpus,
so they will fit even if they "waste" some bits during parsing.

I'm almost inclined to suggest that if a user wants #vcpus > #pcpus they
should have to specify maxvcpus and not rely on the vnuma parsing code
inferring this fact.

IOW maybe this code could just error out (or print a warning) if this
happens? + a doc update.

> Calculate the maximum number of vcpus before allocating vcpu bitmap.
> This requires parsing the same config options twice. Extra a macro to do
> that.

I'm not sure a macro was really the right answer here. e.g. a function
which takes a pointer to a bitmap, if the bitmap is null return the size
which would be needed, otherwise fill in the bitmap, or something. That
could also be split more obviously into a refactoring step and then the
addition of the new checks.

> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> ---
> Valgrind is still clean after this patch applied.
> 
> This patch looks massive because it involves indentation changes, but in
> fact the meat of it is small.

Even with -b it's impossible to read.

Ian.

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