Re: [Xen-devel] [PATCH v10 6/6] tools: enable Cache QoS Monitoring feature for libxl/libxc

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2014-04-03 at 11:31 +0000, Xu, Dongxiao wrote:
> > -----Original Message-----
> > From: Ian Campbell [mailto:Ian.Campbell@xxxxxxxxxx]
> > Sent: Friday, March 28, 2014 5:44 PM
> > To: Xu, Dongxiao
> > Cc: xen-devel@xxxxxxxxxxxxx; keir@xxxxxxx; JBeulich@xxxxxxxx;
> > Ian.Jackson@xxxxxxxxxxxxx; stefano.stabellini@xxxxxxxxxxxxx;
> > andrew.cooper3@xxxxxxxxxx; konrad.wilk@xxxxxxxxxx; dgdegra@xxxxxxxxxxxxx
> > Subject: Re: [PATCH v10 6/6] tools: enable Cache QoS Monitoring feature for
> > libxl/libxc
> > 
> > On Fri, 2014-03-28 at 00:53 +0000, Xu, Dongxiao wrote:
> > > > -----Original Message-----
> > > > From: Ian Campbell [mailto:Ian.Campbell@xxxxxxxxxx]
> > > > Sent: Thursday, March 27, 2014 11:14 PM
> > > > To: Xu, Dongxiao
> > > > Cc: xen-devel@xxxxxxxxxxxxx; keir@xxxxxxx; JBeulich@xxxxxxxx;
> > > > Ian.Jackson@xxxxxxxxxxxxx; stefano.stabellini@xxxxxxxxxxxxx;
> > > > andrew.cooper3@xxxxxxxxxx; konrad.wilk@xxxxxxxxxx;
> > dgdegra@xxxxxxxxxxxxx
> > > > Subject: Re: [PATCH v10 6/6] tools: enable Cache QoS Monitoring feature 
> > > > for
> > > > libxl/libxc
> > > >
> > > > On Wed, 2014-03-26 at 14:35 +0800, Dongxiao Xu wrote:
> > > > [...]
> > > > > +int libxl_pqos_attach(libxl_ctx *ctx, uint32_t domid, libxl_pqos_type
> > > > qos_type);
> > > > > +int libxl_pqos_detach(libxl_ctx *ctx, uint32_t domid, libxl_pqos_type
> > > > qos_type);
> > > > > +libxl_cqminfo * libxl_getcqminfo(libxl_ctx *ctx, unsigned int 
> > > > > *l3c_total,
> > > > > +    unsigned int *nr_domains, unsigned int *nr_rmids, unsigned int
> > > > *nr_sockets);
> > > > [...]
> > > > > +libxl_cqminfo = Struct("cqminfo", [
> > > > > +    ("valid",         uint32),
> > > > > +    ("l3c",           uint64),
> > > > > +    ])
> > > >
> > > > libxl_getcqminfo seems to have a strange mixture of returning an info
> > > > struct and returning things via pointers passed as integers. why is
> > > > that?
> > >
> > > The returned info is a unit data structure containing the L3 cache usage 
> > > data for
> > certain RMID on certain socket.
> > > These pointers passed integers tell caller the number of such units are
> > returned.
> > >
> > > This follows one existing function:
> > > libxl_dominfo * libxl_list_domain(libxl_ctx *ctx, int *nb_domain_out);
> > > where the return value is the unit dominfo data structure, and
> > *nb_domain_out tells caller how many data structure units are returned.
> > 
> > But libxl_getqminfo has three such nr_* pointers as parameters, which
> > one is the length of the returned array? What are the other two? How
> > does one enumerate the things which the other nr_* refer to?
> 
> The size is calculated by nr_domains*nr_sockets. The nr_rmids is to
> show how many RMIDs a system has.

How do I find the info for socket i and domain j then?

Please can you add a doc comment to this function to explain.

Is domains in this context a Xen domain or some other type of hardware
related domain?

Or maybe the result of this function should be something more structured
like:

        struct cqpcpuinfo {
                uint??_t socket, domain;
                uint32_t valid; /* why not a bool? */
                uint32_t l3c;
        };
        struct cqminfo {
                int nr_rmids;
                int nr_sockets;
                int nr_domains;
                cqmcpuifo *info; /* indexed by ...
        };
?

Or even a three level thing with top-level, sockets and domains (or
domains then sockets):
        struct cqminfo {
                ...
                int nr_sockets
                struct cqsocketinfo {
                        int nr_domains
                        ...
                }
        }

Also can valid be a bool? and what is "l3c", I guess it has something to
do with the l3 cache, but please can you name it something more
descriptive.



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