KVM Archive on lore.kernel.org
 help / color / Atom feed
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
Message-ID: <20200113071648.GF19995@umbus> (raw)
In-Reply-To: <20200110105055.3e72ddf4@bahia.lan>

[-- Attachment #1: Type: text/plain, Size: 1842 bytes --]

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

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]

  parent reply index

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

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200113071648.GF19995@umbus \
    --to=david@gibson.dropbear.id.au \
    --cc=alistair.francis@wdc.com \
    --cc=dgilbert@redhat.com \
    --cc=eblake@redhat.com \
    --cc=ehabkost@redhat.com \
    --cc=groug@kaod.org \
    --cc=kvm@vger.kernel.org \
    --cc=marcel.apfelbaum@gmail.com \
    --cc=mtosatti@redhat.com \
    --cc=pbonzini@redhat.com \
    --cc=peter.maydell@linaro.org \
    --cc=philmd@redhat.com \
    --cc=qemu-arm@nongnu.org \
    --cc=qemu-devel@nongnu.org \
    --cc=qemu-ppc@nongnu.org \
    --cc=quintela@redhat.com \
    --cc=rth@twiddle.net \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

KVM Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/kvm/0 kvm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 kvm kvm/ https://lore.kernel.org/kvm \
		kvm@vger.kernel.org
	public-inbox-index kvm

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.kvm


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git