RE: [PATCH v2 1/5] hw: Add sockets_specified field in CpuTopology

[Anup Patel]

> -----Original Message-----
> From: Daniel P. Berrangé <address@hidden>
> Sent: 27 May 2020 15:21
> To: Anup Patel <address@hidden>
> Cc: Eduardo Habkost <address@hidden>; Marcel Apfelbaum
> <address@hidden>; Peter Maydell <address@hidden>;
> Palmer Dabbelt <address@hidden>; Alistair Francis
> <address@hidden>; Sagar Karandikar <address@hidden>;
> Atish Patra <address@hidden>; address@hidden; qemu-
> address@hidden; Anup Patel <address@hidden>
> Subject: Re: [PATCH v2 1/5] hw: Add sockets_specified field in CpuTopology
> 
> On Wed, May 27, 2020 at 09:48:39AM +0000, Anup Patel wrote:
> >
> >
> > > -----Original Message-----
> > > From: Daniel P. Berrangé <address@hidden>
> > > Sent: 27 May 2020 14:16
> > > To: Anup Patel <address@hidden>
> > > Cc: Eduardo Habkost <address@hidden>; Marcel Apfelbaum
> > > <address@hidden>; Peter Maydell
> > > <address@hidden>; Palmer Dabbelt <address@hidden>;
> > > Alistair Francis <address@hidden>; Sagar Karandikar
> > > <address@hidden>; Atish Patra <address@hidden>;
> > > address@hidden; qemu- address@hidden; Anup Patel
> > > <address@hidden>
> > > Subject: Re: [PATCH v2 1/5] hw: Add sockets_specified field in
> > > CpuTopology
> > >
> > > On Wed, May 27, 2020 at 11:12:22AM +0530, Anup Patel wrote:
> > > > When "sockets" sub-option of "-smp" option is not specified, the
> > > > smp_parse() function will assume one CPU per-socket and set the
> > > > number of sockets equal to number of CPUs.
> > > >
> > > > This is counter-intuitive and we should allow machine emulation to
> > > > decide default number of sockets when "sockets" sub-option is not
> > > > specified.
> > >
> > > I don't agree with this.  Having the semantics of the -smp option be
> > > the same across all targets/machines *is* intuitive.  Changing
> > > semantics of -smp per- machine will create a worse experiance for
> > > people configuring QEMU as the configuration will mean different things
> depending on the machine choce.
> >
> > Okay then why don't we default to sockets=1 in smp_parse() when "sockets"
> > sub-options is not specified ?? This will make it uniform across machines.
> >
> > Is there a reason to by default have sockets=max_cpus ??
> 
> IIUC both of these questions are due to backwards compatibility with pre-
> existing QEMU versions.

I see that hw/x86/pc.c implements it's own smp_parse() callback.
Can we take that route ??

We need to have sockets=1 by default for RISC-V machines because
each socket has it's own interrupt controller and other peripherals.

Regards,
Anup