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Re: [Qemu-devel] [PATCH] vl.c: Check max_cpus limit instead of smp_cpus

From: Eduardo Habkost
Subject: Re: [Qemu-devel] [PATCH] vl.c: Check max_cpus limit instead of smp_cpus
Date: Thu, 8 May 2014 15:46:40 -0300
User-agent: Mutt/1.5.21 (2010-09-15)

On Thu, May 08, 2014 at 04:07:54PM +0100, Peter Maydell wrote:
> On 8 May 2014 16:00, Eduardo Habkost <address@hidden> wrote:
> > On Thu, May 08, 2014 at 09:26:36AM +0100, Peter Maydell wrote:
> >> On 7 May 2014 23:20, Andreas Färber <address@hidden> wrote:
> >> > Am 07.05.2014 23:48, schrieb Peter Maydell:
> >> >> This is confusing. What is max_cpus
> >> >
> >> > Specified via -smp, defaults to actual CPUs.
> >>
> >> I thought that was smp_cpus ...
> >
> > smp_cpus is the first argument to -smp. max_cpus is the "maxcpus" option
> > of -smp.
> > Please don't do this. If the maxcpus value from the command-line is not
> > supported, QEMU should abort instead of silently ignoring the value
> > provided by the user.
> Ah, I see. This code is confusing because we've split the
> handling of user errors in the -smp argument between
> the smp_parse() function and this bit of inline code.
> Ideally we should put all the error handling in one
> place...

The split makes sense to me: smp_parse() is just for basic parsing that
doesn't depend on any state other than the provided QemuOpts parameter,
and can run at any point in time.

The machine->max_cpus check, on the other hand depend on the machine
object to be created, and even changes the machine->max_cpus value. It
is more dependent on ordering of initialization. To me, it makes sense
to have it outside smp_parse().

But while looking at that code, I noticed that we can at least make the
MAX_CPUMASK_BITS check and the machine->max_cpus check a single one. I
will send a new patch.


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