Re: [Xen-devel] [PATCH v3 06/15] x86: implement get value interface for MBA

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Wed, Sep 20, 2017 at 05:22:22PM +0800, Yi Sun wrote:
> On 17-09-20 09:43:40, Roger Pau Monn� wrote:
> > On Wed, Sep 20, 2017 at 01:09:06PM +0800, Yi Sun wrote:
> > > On 17-09-19 10:15:42, Roger Pau Monn� wrote:
> > > > On Tue, Sep 05, 2017 at 05:32:28PM +0800, Yi Sun wrote:
> > > > > diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
> > > > > index 696eff2..7902af7 100644
> > > > > --- a/xen/arch/x86/domctl.c
> > > > > +++ b/xen/arch/x86/domctl.c
> > > > > @@ -1496,6 +1496,13 @@ long arch_do_domctl(
> > > > >              copyback = true;
> > > > >              break;
> > > > >  
> > > > > +        case XEN_DOMCTL_PSR_ALLOC_GET_MBA_THRTL:
> > > > > +            ret = psr_get_val(d, domctl->u.psr_alloc.target,
> > > > > +                              &val32, PSR_TYPE_MBA_THRTL);
> > > > > +            domctl->u.psr_alloc.data = val32;
> > > > 
> > > > Hm, why does psr_get_val take a uint32_t * instead of a uint64_t *? So
> > > > that you can directly pass &domctl->u.psr_alloc.data.
> > > > 
> > > > Or the other way around, why is domctl->u.psr_alloc.data a uint64_t
> > > > instead of a uint32_t?
> > > > 
> > > There is a historical reason. The COS MSR is 64bit. So, the original codes
> > > in L3 CAT (submitted years ago) used uint64_t.
> > > 
> > > But during L2 CAT review, per Jan's comment, the uint64_t is not necessary
> > > in psr.c. So, we convert it to uint32_t in psr.c and make the codes you 
> > > see
> > > here.
> > 
> > Since this is a DOMCTL, you can change the type of the structure to be
> > an uint32_t, so that you can pass it directly (unless I'm missing
> > something else that requires this to be uint64_t).
> > 
> The tools layer implementation uses uint64_t according to SDM definition. So,
> we have to do a convertion here or in tools/. Or, we need modify interfaces in
> tools layer.
> 
> As CAT interfaces in tools layer have been released and it is a natural choice
> to make it same as SDM, I think should keep uint64_t in tools at least. If so,
> we must do the convertion somewhere. Then, I think it is not so necessary to
> change current codes. Is that good to you?

You can change libxc interfaces at will, you need to pay more attention
if you change libxl. This is just FYI. I'm not suggesting you have to
change the interfaces.

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