Re: [Xen-devel] [PATCH RESEND v5 01/24] docs: create L2 Cache Allocation Technology (CAT) feature document

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Yi Sun [mailto:yi.y.sun@xxxxxxxxxxxxxxx]
> Sent: Sunday, January 22, 2017 10:15 AM
> 
> > > +
> > > +     New option `-l` is added.
> > > +     `-l2`: Specify cbm for L2 cache.
> > > +     `-l3`: Specify cbm for L3 cache.
> > > +
> > > +     If neither `-l2` nor `-l3` is given, level 3 is the default option.
> > > +
> > > +  3. `psr-hwinfo [OPTIONS]`:
> > > +
> > > +     Show L2 & L3 CAT HW informations on every socket.
> >
> > informations -> information
> >
> > and which HW information? please elaborate.
> >
> > and where is the interface of setting COS for VCPU?
> >
> What do you mean 'the interface of setting COS for VCPU'? User can set CBM
> for one domain through 'psr-cat-cbm-set' now. Then, hypervisor will find
> a matched COS ID or pick an available COS ID for the domain. User does not
> need know which COS ID it is using.

possibly you want to explain above logic in this doc. I didn't see any
discussion of COS ID in the text.

> 
> > > +
> > > +* Multi-sockets
> > > +
> > > +  Different sockets may have different L2 CAT capability (e.g. max COS)
> > > +  although it is consistent on the same socket. So the capability of
> > > +  per-socket L2 CAT is specified.
> >
> > VCPU schedule design is important here. e.g. when migrating a VCPU
> > from socket 1 to socket 2 (socket 1 has max COS as 16 while socket
> > 2 as 8), will you prevent migration if VCPU has a COS (9)?
> >
> 'psr-cat-cbm-set' can set CBM for one domain per socket. On each socket, we
> maintain a COS array for all domains. One domain uses one COS at one time. One
> COS saves the CBM of to work. So, when a VCPU of the domain is migrated from
> socket 1 to socket 2, it follows configuration on socket 2. This mechanism has
> been implemented since L3 CAT. L2 CAT follows it.
> 
> E.g. user sets domain 1 CBM on socket 1 to 0x7f which uses COS 9 but sets
> domain 1 CBM on socket 2 to 0x3f which uses COS 7. When VCPU of this domain
> is migrated from socket 1 to 2, the COS ID used will be 7, that means 0x3f
> will be the CBM to work for this domain.

OK, so user will pick valid CBM on each socket for a specific domain. Also
please include such info in your next version.

Thanks
Kevin
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