On Fri, 6 Oct 2017 15:06:57 -0700
Alistair Francis <alistair.fran...@xilinx.com> wrote:
> On Fri, Oct 6, 2017 at 4:45 AM, Eduardo Habkost <ehabk...@redhat.com> wrote:
> > On Fri, Oct 06, 2017 at 10:23:12AM +0200, Igor Mammedov wrote:
> >> On Thu, 5 Oct 2017 14:09:06 -0300
> >> Eduardo Habkost <ehabk...@redhat.com> wrote:
> >>
> >> > On Thu, Oct 05, 2017 at 11:04:27AM +0200, Igor Mammedov wrote:
> >> > > On Wed, 4 Oct 2017 14:39:20 -0700
> >> > > Alistair Francis <alistair.fran...@xilinx.com> wrote:
> >> > >
> >> > > > On Wed, Oct 4, 2017 at 9:34 AM, Eduardo Habkost
> >> > > > <ehabk...@redhat.com> wrote:
> >> > > > > On Wed, Oct 04, 2017 at 03:08:16PM +0200, Igor Mammedov wrote:
> >> > > > >> On Wed, 4 Oct 2017 09:28:51 -0300
> >> > > > >> Eduardo Habkost <ehabk...@redhat.com> wrote:
> >> > > > >>
> >> > > > >> > On Wed, Oct 04, 2017 at 01:12:32PM +0200, Igor Mammedov wrote:
> >> > > > >> > > On Tue, 3 Oct 2017 14:41:17 -0700
> >> > > > >> > > Alistair Francis <alistair.fran...@xilinx.com> wrote:
> >> > > > >> > >
> >> > > > >> > > > On Tue, Oct 3, 2017 at 1:36 PM, Eduardo Habkost
> >> > > > >> > > > <ehabk...@redhat.com> wrote:
> >> > > > >> > > > > On Tue, Oct 03, 2017 at 01:05:13PM -0700, Alistair
> >> > > > >> > > > > Francis wrote:
> >> > > > >> > > > >> List all possible valid CPU options.
> >> > > > >> > > > >>
> >> > > > >> > > > >> Signed-off-by: Alistair Francis
> >> > > > >> > > > >> <alistair.fran...@xilinx.com>
> >> > > > >> > > > >> ---
> >> > > > >> > > > >>
> >> > > > >> > > > >> hw/arm/xlnx-zcu102.c | 10 ++++++++++
> >> > > > >> > > > >> hw/arm/xlnx-zynqmp.c | 16 +++++++++-------
> >> > > > >> > > > >> include/hw/arm/xlnx-zynqmp.h | 1 +
> >> > > > >> > > > >> 3 files changed, 20 insertions(+), 7 deletions(-)
> >> > > > >> > > > >>
> >> > > > >> > > > >> diff --git a/hw/arm/xlnx-zcu102.c b/hw/arm/xlnx-zcu102.c
> >> > > > >> > > > >> index 519a16ed98..039649e522 100644
> >> > > > >> > > > >> --- a/hw/arm/xlnx-zcu102.c
> >> > > > >> > > > >> +++ b/hw/arm/xlnx-zcu102.c
> >> > > > >> > > > >> @@ -98,6 +98,8 @@ static void
> >> > > > >> > > > >> xlnx_zynqmp_init(XlnxZCU102 *s, MachineState *machine)
> >> > > > >> > > > >> object_property_add_child(OBJECT(machine), "soc",
> >> > > > >> > > > >> OBJECT(&s->soc),
> >> > > > >> > > > >> &error_abort);
> >> > > > >> > > > >>
> >> > > > >> > > > >> + object_property_set_str(OBJECT(&s->soc),
> >> > > > >> > > > >> machine->cpu_type, "cpu-type",
> >> > > > >> > > > >> + &error_fatal);
> >> > > > >> > > > >
> >> > > > >> > > > > Do you have plans to support other CPU types to
> >> > > > >> > > > > xlnx_zynqmp in
> >> > > > >> > > > > the future? If not, I wouldn't bother adding the cpu-type
> >> > > > >> > > > > property and the extra boilerplate code if it's always
> >> > > > >> > > > > going to
> >> > > > >> > > > > be set to cortex-a53.
> >> > > > >> > > >
> >> > > > >> > > > No, it'll always be A53.
> >> > > > >> > > >
> >> > > > >> > > > I did think of that, but I also wanted to use the new
> >> > > > >> > > > option! I also
> >> > > > >> > > > think there is an advantage in sanely handling users '-cpu'
> >> > > > >> > > > option,
> >> > > > >> > > > before now we just ignored it, so I think it still does
> >> > > > >> > > > give a
> >> > > > >> > > > benefit. That'll be especially important on the Xilinx tree
> >> > > > >> > > > (sometimes
> >> > > > >> > > > people use our machines with a different CPU to 'benchmark'
> >> > > > >> > > > or test
> >> > > > >> > > > other CPUs with our CoSimulation setup). So I think it does
> >> > > > >> > > > make sense
> >> > > > >> > > > to keep in.
> >> > > > >> > > if cpu isn't user settable, one could just outright die if
> >> > > > >> > > cpu_type
> >> > > > >> > > is not NULL and say that user's CLI is wrong.
> >> > > > >> > > (i.e. don't give users illusion that they allowed to use
> >> > > > >> > > '-cpu')
> >> > > > >> >
> >> > > > >> > Isn't it exactly what this patch does, by setting:
> >> > > > >> > mc->default_cpu_type = ARM_CPU_TYPE_NAME("cortex-a53");
> >> > > > >> > mc->valid_cpu_types = xlnx_zynqmp_valid_cpus;
> >> > > > >> > ?
> >> > > > >> >
> >> > > > >> > Except that "-cpu cortex-a53" won't die, which is a good thing.
> >> > > > >> >
> >> > > > >> allowing "-cpu cortex-a53" here, would allow to use feature
> >> > > > >> parsing
> >> > > > >> which weren't allowed or were ignored before if user supplied
> >> > > > >> '-cpu'.
> >> > > > >> so I'd more strict and refuse any -cpu and break CLI that tries
> >> > > > >> to use it
> >> > > > >> if board has non configurable cpu type. It would be easier to
> >> > > > >> relax
> >> > > > >> restriction later if necessary.
> >> > > > >>
> >> > > > >> using validate_cpus here just to have users for the new code,
> >> > > > >> doesn't seem like valid justification and at that it makes board
> >> > > > >> code more complex where it's not necessary and build in cpu type
> >> > > > >> works just fine.
> >> > > > >
> >> > > > > It's up to the board maintainer to decide what's the best option.
> >> > > > > Both features are independent from each other and can be
> >> > > > > implemented by machine core.
> >> > > >
> >> > > > Noooo!
> >> > > >
> >> > > > My hope with this series is that eventually we could hit a state
> >> > > > where
> >> > > > every single machine acts the same way with the -cpu option.
> >> > > >
> >> > > > I really don't like what we do now where some boards use it, some
> >> > > > boards error and some boars just ignore the option. I think we should
> >> > > > agree on something and every machine should follow the same flow so
> >> > > > that users know what to expect when they use the -cpu option.
> >> > > >
> >> > > > If this means we allow machines to specify they don't support the
> >> > > > option or only have a single element in the list of supported options
> >> > > > doesn't really matter, but all machines should do the same thing.
> >> > > >
> >> > > > >
> >> > > > > In either case, the valid_cpu_types feature will be still very
> >> > > > > useful for boards like pxa270 and sa1110, which support -cpu but
> >> > > > > only with specific families of CPU types (grep for
> >> > > > > "strncmp(cpu_type").
> >> > > > >
> >> > > > >>
> >> > > > >> wrt centralized way to refuse -cpu if board doesn't support it,
> >> > > > >> (which is not really related to this series) following could be
> >> > > > >> done:
> >> > > > >>
> >> > > > >> when cpu_model removal is completely done I plan to replace
> >> > > > >> vl.c
> >> > > > >> cpu_parse_cpu_model(machine_class->default_cpu_type,
> >> > > > >> cpu_model)
> >> > > > >> with
> >> > > > >> cpu_parse_cpu_model(DEFAULT_TARGET_CPU_TYPE, cpu_model)
> >> > > > >>
> >> > > > >> so that we could drop temporary guard
> >> > > > >>
> >> > > > >> if (machine_class->default_cpu_type) {
> >> > > > >
> >> > > > > This sounds good to me, even if we don't reject -cpu on any
> >> > > > > board.
> >> > > > >
> >> > > > >
> >> > > > >>
> >> > > > >> with that it would be possible to tell from
> >> > > > >> machine_run_board_init()
> >> > > > >> that board doesn't provide cpu but user provided '-cpu'
> >> > > > >> so we would be able to:
> >> > > > >> if ((machine_class->default_cpu_type == NULL) &&
> >> > > > >> (machine->cpu_type != NULL))
> >> > > > >> error_fatal("machine doesn't support -cpu option");
> >> > > > >
> >> > > > > I won't complain too much if a board maintainer really wants to
> >> > > > > make the board reject -cpu completely, but it's up to them.
> >> > > >
> >> > > > I disagree. I think a standard way of doing it is better. At least
> >> > > > for
> >> > > > each architecture. The ARM -cpu option is very confusing at the
> >> > > > moment
> >> > > > and it really doesn't need to be that bad.
> >> > > >
> >> > > > >
> >> > > > > Personally, I'd prefer to have all boards setting
> >> > > > > default_cpu_type even if they support only one CPU model, so
> >> > > > > clients don't need a special case for boards that don't support
> >> > > > > -cpu.
> >> > > >
> >> > > > I agree, I think having one CPU makes more sense. It makes it easier
> >> > > > to add support for more cpus in the future and allows the users to
> >> > > > use
> >> > > > the -cpu option without killing QEMU.
> >> > > I'm considering -cpu option as a legacy one that server 2 purposes now
> >> > >
> >> >
> >> > I'm not sure about "legacy", but the list of purposes looks
> >> > accurate:
> >> >
> >> > > 1: pick cpu type for running instance
> >> >
> >> > This one has no replacement yet, so can we really call it legacy?
> >> not really, it's not going anywhere in near future
> >>
> >> >
> >> > > 2: convert optional features/legacy syntax to global properties
> >> > > for related cpu type
> >> >
> >> > This one has a replacement: -global. But there's a difference
> >> > between saying "-cpu features are implemented using -global" and
> >> > "-cpu features are obsoleted by -global". I don't think we can
> >> > say it's obsolete or legacy unless existing management software
> >> > is changed to be using something else.
> >> >
> >> >
> >> > >
> >> > > It plays ok for machines with single type of cpu but doesn't really
> >> > > scale
> >> > > to more and doesn't work well nor needed if we were to specify cpus on
> >> > > CLI
> >> > > with -device (i.e. build machine from config/CLI)
> >> >
> >> > This is a good point. But -cpu is still a useful shortcut for
> >> > boards that have a single CPU type. What are the arguments we
> >> > have to get rid of it completely?
> >> boards that have single cpu type don't need -cpu. since cpu is not
> >> configurable there.
> >
> > They don't need -cpu, but there's no need to reject "-cpu FOO" if
> > we know FOO is the CPU model used by the board. This is the only
> > difference between what you propose and what Alistair proposes,
> > right?
> >
> >
> >>
> >>
> >> > > So I would not extend usage '-cpu' to boards that have fixed cpu type,
> >> > > because it really useless in that case and confuses users with idea
> >> > > that
> >> > > they have ability/need to specify -cpu on fixed cpu board.
> >> >
> >> > If they try to choose any other CPU model, they will see an error
> >> > message explicitly saying only one CPU type is supported. What
> >> > would be the harm?
> >> I guess I've already pointed drawbacks from interface point of view,
> >> from maintainer pov it will be extra code to maintain valid cpus
> >> vs just 'create_cpu(MY_CPU_TYPE)'
> >> this patch is vivid example of the case
> >
> > With this part I agree. We don't need to add boilerplate code to
> > board init if the CPU model will always be the same.
> >
> > But I would still prefer to do this:
> >
> > create_cpu(MY_CPU_TYPE); // at XXX_init()
> > [...]
> > static void xxx_class_init(...) {
> > mc->default_cpu_type = MY_CPU_TYPE;
> > /* Reason: XXX_init() is hardcoded to MY_CPU_TYPE */
> > mc->valid_cpu_types = { MY_CPU_TYPE, NULL };
> > }
>
> I like this option. It doesn't add much code and I think makes it very
> clear to users.
>
> Another thing to point out is that I see users specifying options to
> QEMU all the time that QEMU will just ignore. Imagine people see
> somewhere online that others use '-cpu' and suddenly they think they
> have to. Having this throw an error that '-cpu' isn't supported in
> this case (but is in others) will create confusion of when it
> should/shouldn't be use. I think always allowing it and telling users
> the supported CPUs clears this up.
patch would look better with what Eduardo suggested above.
at least it will minimize amount of not need code, so I'd go for it.
