From: David Gibson <david@gibson.dropbear.id.au>
To: Greg Kurz <groug@kaod.org>
Cc: "Philippe Mathieu-Daudé" <philmd@redhat.com>,
qemu-devel@nongnu.org, "Peter Maydell" <peter.maydell@linaro.org>,
"Eduardo Habkost" <ehabkost@redhat.com>,
kvm@vger.kernel.org, "Juan Quintela" <quintela@redhat.com>,
qemu-ppc@nongnu.org, "Marcelo Tosatti" <mtosatti@redhat.com>,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
qemu-arm@nongnu.org,
"Alistair Francis" <alistair.francis@wdc.com>,
"Marcel Apfelbaum" <marcel.apfelbaum@gmail.com>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Richard Henderson" <rth@twiddle.net>,
"Eric Blake" <eblake@redhat.com>
Subject: Re: [PATCH 04/15] hw/ppc/spapr_rtas: Restrict variables scope to single switch case
Date: Mon, 13 Jan 2020 17:16:48 +1000 [thread overview]
Message-ID: <20200113071648.GF19995@umbus> (raw)
In-Reply-To: <20200110105055.3e72ddf4@bahia.lan>
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On Fri, Jan 10, 2020 at 10:50:55AM +0100, Greg Kurz wrote:
> On Fri, 10 Jan 2020 10:34:07 +0100
> Philippe Mathieu-Daudé <philmd@redhat.com> wrote:
>
> > On 1/9/20 6:43 PM, Greg Kurz wrote:
> > > On Thu, 9 Jan 2020 16:21:22 +0100
> > > Philippe Mathieu-Daudé <philmd@redhat.com> wrote:
> > >
> > >> We only access these variables in RTAS_SYSPARM_SPLPAR_CHARACTERISTICS
> > >> case, restrict their scope to avoid unnecessary initialization.
> > >>
> > >
> > > I guess a decent compiler can be smart enough detect that the initialization
> > > isn't needed outside of the RTAS_SYSPARM_SPLPAR_CHARACTERISTICS branch...
> > > Anyway, reducing scope isn't bad. The only hitch I could see is that some
> > > people do prefer to have all variables declared upfront, but there's a nested
> > > param_val variable already so I guess it's okay.
> >
> > I don't want to outsmart compilers :)
> >
> > The MACHINE() macro is not a simple cast, it does object introspection
> > with OBJECT_CHECK(), thus is not free. Since
>
> Sure, I understand the motivation in avoiding an unneeded call
> to calling object_dynamic_cast_assert().
>
> > object_dynamic_cast_assert() argument is not const, I'm not sure the
> > compiler can remove the call.
> >
>
> Not remove the call, but delay it to the branch that uses it,
> ie. parameter == RTAS_SYSPARM_SPLPAR_CHARACTERISTICS.
I think any performance consideration here is a red herring. This
particular RTAS call is a handful-of-times-per-boot thing, and only
AFAIK used by AIX guests.
I'm in favour of the change on the grounds of code locality and
readability.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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next prev parent reply other threads:[~2020-01-13 7:17 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-09 15:21 [PATCH 00/15] Replace current_machine by qdev_get_machine() Philippe Mathieu-Daudé
2020-01-09 15:21 ` [PATCH 01/15] target/arm/kvm: Use CPUState::kvm_state in kvm_arm_pmu_supported() Philippe Mathieu-Daudé
2020-01-10 9:59 ` Alistair Francis
2020-01-09 15:21 ` [PATCH 02/15] hw/ppc/spapr_rtas: Use local MachineState variable Philippe Mathieu-Daudé
2020-01-09 17:13 ` Greg Kurz
2020-01-13 1:11 ` David Gibson
2020-01-09 15:21 ` [PATCH 03/15] hw/ppc/spapr_rtas: Access MachineState via SpaprMachineState argument Philippe Mathieu-Daudé
2020-01-09 17:13 ` Greg Kurz
2020-01-13 1:11 ` David Gibson
2020-01-09 15:21 ` [PATCH 04/15] hw/ppc/spapr_rtas: Restrict variables scope to single switch case Philippe Mathieu-Daudé
2020-01-09 17:43 ` Greg Kurz
2020-01-10 9:34 ` Philippe Mathieu-Daudé
2020-01-10 9:50 ` Greg Kurz
2020-01-10 19:18 ` Eric Blake
2020-01-13 7:16 ` David Gibson [this message]
2020-01-09 15:21 ` [PATCH 05/15] device-hotplug: Replace current_machine by qdev_get_machine() Philippe Mathieu-Daudé
2020-01-12 9:42 ` Alistair Francis
2020-01-09 15:21 ` [PATCH 06/15] migration/savevm: " Philippe Mathieu-Daudé
2020-01-09 15:52 ` Dr. David Alan Gilbert
2020-01-12 9:43 ` Alistair Francis
2020-01-14 13:27 ` Juan Quintela
2020-01-09 15:21 ` [PATCH 07/15] hw/core/machine-qmp-cmds: " Philippe Mathieu-Daudé
2020-01-12 9:44 ` Alistair Francis
2020-01-09 15:21 ` [PATCH 08/15] target/arm/monitor: " Philippe Mathieu-Daudé
2020-01-12 9:47 ` Alistair Francis
2020-01-09 15:21 ` [PATCH 09/15] device_tree: " Philippe Mathieu-Daudé
2020-01-12 9:47 ` Alistair Francis
2020-01-09 15:21 ` [PATCH 10/15] memory: " Philippe Mathieu-Daudé
2020-01-12 9:48 ` Alistair Francis
2020-01-12 13:45 ` Philippe Mathieu-Daudé
2020-01-14 2:02 ` Alistair Francis
2020-01-09 15:21 ` [PATCH 11/15] exec: " Philippe Mathieu-Daudé
2020-01-14 1:57 ` Alistair Francis
2020-01-09 15:21 ` [PATCH 12/15] accel: Introduce the current_accel() method Philippe Mathieu-Daudé
2020-01-14 1:59 ` Alistair Francis
2020-01-09 15:21 ` [PATCH 13/15] accel: Replace current_machine->accelerator by " Philippe Mathieu-Daudé
2020-01-14 1:58 ` Alistair Francis
2020-01-09 15:21 ` [PATCH 14/15] accel/accel: Replace current_machine by qdev_get_machine() Philippe Mathieu-Daudé
2020-01-14 1:59 ` Alistair Francis
2020-01-09 15:21 ` [PATCH 15/15] vl: Make current_machine a local variable Philippe Mathieu-Daudé
2020-01-14 2:00 ` Alistair Francis
2020-01-21 8:59 ` [PATCH 00/15] Replace current_machine by qdev_get_machine() Markus Armbruster
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