Re: [Xen-devel] [PATCH v8 2/5] tools: add routine to get CMT L3 event mask

[Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>]

On Wed, Jan 28, 2015 at 01:40:25PM +0000, Ian Campbell wrote:
> On Wed, 2015-01-28 at 16:04 +0800, Chao Peng wrote:
> > This is the tools side wrapper for XEN_SYSCTL_PSR_CMT_get_l3_event_mask
> > of XEN_SYSCTL_psr_cmt_op.
> > 
> > Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
> > ---
> >  tools/libxc/include/xenctrl.h |  1 +
> >  tools/libxc/xc_psr.c          | 17 +++++++++++++++++
> >  tools/libxl/libxl.h           |  1 +
> 
> This needs a LIBXL_HAVE #define in libxl.h to advertise the new
> functionality.
OK.
> 
> > +int xc_psr_cmt_get_l3_event_mask(xc_interface *xch, uint32_t *event_mask);
> 
> What are the possible values of the event mask? Is there a guarantee
> from somewhere that 32-bits is always sufficient?

It comes directly from cpuid which is 32 bit now and look like not
possible to extend it to 64 bit. Only bits[0:2] is used at present.

> 
> How can the libxl caller decode the meaning of the bits since they are
> not defined in the libxl.h header?
> 
> Perhaps a struct of booleans would be a better interface at the libxl
> level?
> 
> Or perhaps the interface should be more along the lines of "is psr
> feature X available", like libxl_psr_..._feature_enabled(ctx,
> SOME_SYMBOL)?
> 
> Or perhaps the function to actual access the info should have an
> ERROR_PSR_FUNCTION NOT_SUPPORTED return?

As answered in another reply, I'd use it as:
int libxl_psr_cmt_type_supported(libxl_ctx *ctx, libxl_psr_cmt_type type);

Thanks,
Chao

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