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

[Daniel P . Berrangé]

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.


Regards,
Daniel
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