Re: [Xen-devel] [PATCH v3 11/14] libxl: get and set soft affinity

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2013-11-20 at 11:29 +0000, George Dunlap wrote:
> On 20/11/13 11:27, Ian Campbell wrote:
> > On Tue, 2013-11-19 at 18:51 +0100, Dario Faggioli wrote:
> >>>> +{
> >>>> +    libxl_cputopology *topology;
> >>>> +    libxl_bitmap ecpumap;
> >>>> +    int nr_cpus = 0, rc;
> >>>> +
> >>>> +    topology = libxl_get_cpu_topology(ctx, &nr_cpus);
> >>>> +    if (!topology) {
> >>>> +        LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "failed to retrieve CPU 
> >>>> topology");
> >>> It's not consistent within the file but I think for new functions we
> >>> should use the LOG macro variants.
> >>>
> >> Right, but don't I need a gc to use it? Should I "make up" one just for
> >> the purpose of using LOG/LOGE?
> > I think a call to GC_INIT/GC_FREE should be cheap enough.
> >
> >>>> +        return ERROR_FAIL;
> >>>> +    }
> >>>> +    libxl_cputopology_list_free(topology, nr_cpus);
> >>> Why are you retrieving this only to immediately throw it away?
> >>>
> >> Because I need nr_cpus. :-)
> > Surely this is not the recommended way to get nr_cpus!
> >
> > libxl_get_cpu_topology() itself calls libxl_get_max_cpus() which seems
> > like the obvious candidate.
> >
> >
> >>>> diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
> >>>> index c7dceda..504c57b 100644
> >>>> --- a/tools/libxl/libxl.h
> >>>> +++ b/tools/libxl/libxl.h
> >>>> @@ -82,6 +82,20 @@
> >>>>   #define LIBXL_HAVE_DOMAIN_NODEAFFINITY 1
> >>>>   
> >>>>   /*
> >>>> + * LIBXL_HAVE_VCPUINFO_SOFTAFFINITY indicates that a 'cpumap_soft'
> >>>> + * field (of libxl_bitmap type) is present in libxl_vcpuinfo,
> >>>> + * containing the soft affinity for the vcpu.
> >>>> + */
> >>>> +#define LIBXL_HAVE_VCPUINFO_SOFTAFFINITY 1
> >>>> +
> >>>> +/*
> >>>> + * LIBXL_HAVE_BUILDINFO_SOFTAFFINITY indicates that a 'cpumap_soft'
> >>>> + * field (of libxl_bitmap type) is present in libxl_domain_build_info,
> >>>> + * containing the soft affinity for the vcpu.
> >>>> + */
> >>>> +#define LIBXL_HAVE_BUILDINFO_SOFTAFFINITY 1
> >>> Given that they arrive can we just use HAVE_SOFTRAFFINITY?
> >>>
> >> You mean just introducing one #define? Sure... For some reason I assumed
> >> that every new field should come with it's own symbol. But if it's fine
> >> to have one, I'm all for it. :-)
> > I think it's ok.
> >
> >>>> +/* Flags, consistent with domctl.h */
> >>>> +#define LIBXL_VCPUAFFINITY_HARD 1
> >>>> +#define LIBXL_VCPUAFFINITY_SOFT 2
> >>> Can these be an enum in the idl?
> >>>
> >> I think yes.
> >>
> >> I did actually check and, of all the enum-s in the IDL, none are used as
> >> flags, they're rather used as "single values". OTOH, the only actual
> >> flags I found (I think it was LIBXL_SUSPEND_DEBUG, LIBXL_SUSPEND_LIVE)
> >> were defined like I did myself above... That's why I went for it.
> > I have a feeling they predate the IDL, or at least the Enumeration
> > support. It's true that we don't have any other bit fields in enums
> > though. I can't see the harm, it's probably not worth introducing a new
> > IDL type for them.
> 
> Since these are bits, not numbers, I don't think an enum is the right 
> construct.  Or, the enum values should be the *bit numbers*, and the 
> flags should be (1<<[bit_humber]).

That would need a new IDL type to express. In which case lets just leave
the raw #defines, unless anyone else has a strong opinion.

Ian.


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