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Wed, 27 May 2020 10:42:12 +0000 (UTC) Date: Wed, 27 May 2020 11:42:09 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Anup Patel Subject: Re: [PATCH v2 1/5] hw: Add sockets_specified field in CpuTopology Message-ID: <20200527104209.GJ2665520@redhat.com> References: <20200527054226.232103-1-anup.patel@wdc.com> <20200527054226.232103-2-anup.patel@wdc.com> <20200527084554.GC2665520@redhat.com> <20200527095123.GH2665520@redhat.com> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.13.4 (2020-02-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.81; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/27 00:45:05 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -10 X-Spam_score: -1.1 X-Spam_bar: - X-Spam_report: (-1.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FROM_EXCESS_BASE64=0.979, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Peter Maydell , "qemu-riscv@nongnu.org" , Eduardo Habkost , Sagar Karandikar , Anup Patel , "qemu-devel@nongnu.org" , Atish Patra , Alistair Francis , Palmer Dabbelt Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, May 27, 2020 at 10:01:21AM +0000, Anup Patel wrote: > > > > -----Original Message----- > > From: Daniel P. Berrangé > > Sent: 27 May 2020 15:21 > > To: Anup Patel > > Cc: Eduardo Habkost ; Marcel Apfelbaum > > ; Peter Maydell ; > > Palmer Dabbelt ; Alistair Francis > > ; Sagar Karandikar ; > > Atish Patra ; qemu-riscv@nongnu.org; qemu- > > devel@nongnu.org; Anup Patel > > Subject: Re: [PATCH v2 1/5] hw: Add sockets_specified field in CpuTopology > > > > On Wed, May 27, 2020 at 09:48:39AM +0000, Anup Patel wrote: > > > > > > > > > > -----Original Message----- > > > > From: Daniel P. Berrangé > > > > Sent: 27 May 2020 14:16 > > > > To: Anup Patel > > > > Cc: Eduardo Habkost ; Marcel Apfelbaum > > > > ; Peter Maydell > > > > ; Palmer Dabbelt ; > > > > Alistair Francis ; Sagar Karandikar > > > > ; Atish Patra ; > > > > qemu-riscv@nongnu.org; qemu- devel@nongnu.org; Anup Patel > > > > > > > > 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. > > I see that hw/x86/pc.c implements it's own smp_parse() callback. > Can we take that route ?? > > We need to have sockets=1 by default for RISC-V machines because > each socket has it's own interrupt controller and other peripherals. I guess the fact that smp_parse() exists as a callback pretty much says that allowing machine type overrides of default semantics is permitted. So yeah, using a smp_parse callback seems reasonable. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|