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bh=ZtIq4WHEhsItahKc+Q4fON6pBjomgpsZmK4vkpQBg9I=; b=cRN1x6chSSyj0An353nMmX1YJNjLvuBJ8lxHwzPCDj6807kqgCvdpel9O8VcG+h1T/4myB 9QhD9qH8IRyheFbc1CkDiOVzJMVL/mUCJKfCAKB4HhUYxSb0ZGnUlyL6V89QJ3bR6+Jrcu +RABT7OF6hzYzYrwEolD4UQYLTig730= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-537-A7KPktYQPEGV6i3m_xkoFA-1; Fri, 16 Jul 2021 05:14:38 -0400 X-MC-Unique: A7KPktYQPEGV6i3m_xkoFA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id AECA81005547; Fri, 16 Jul 2021 09:14:36 +0000 (UTC) Received: from redhat.com (ovpn-115-37.ams2.redhat.com [10.36.115.37]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2180C1981C; Fri, 16 Jul 2021 09:14:29 +0000 (UTC) Date: Fri, 16 Jul 2021 10:14:27 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Cornelia Huck Subject: Re: [PATCH v1 1/9] s390x: smp: s390x dedicated smp parsing Message-ID: References: <1626281596-31061-1-git-send-email-pmorel@linux.ibm.com> <1626281596-31061-2-git-send-email-pmorel@linux.ibm.com> <871r7yd4gf.fsf@redhat.com> MIME-Version: 1.0 In-Reply-To: <871r7yd4gf.fsf@redhat.com> User-Agent: Mutt/2.0.7 (2021-05-04) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Received-SPF: pass client-ip=216.205.24.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.698, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no 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: thuth@redhat.com, ehabkost@redhat.com, Pierre Morel , david@redhat.com, richard.henderson@linaro.org, qemu-devel@nongnu.org, armbru@redhat.com, pasic@linux.ibm.com, borntraeger@de.ibm.com, qemu-s390x@nongnu.org, pbonzini@redhat.com, eblake@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Jul 16, 2021 at 10:54:08AM +0200, Cornelia Huck wrote: > On Wed, Jul 14 2021, Pierre Morel wrote: > > > We need a s390x dedicated SMP parsing to handle s390x specificities. > > > > In this patch we only handle threads, cores and sockets for > > s390x: > > - do not support threads, we always have 1 single thread per core > > - the sockets are filled one after the other with the cores > > > > Both these handlings are different from the standard smp_parse > > functionement and reflect the CPU topology in the simple case > > where all CPU belong to the same book. > > > > Topology levels above sockets, i.e. books, drawers, are not > > considered at this stage and will be introduced in a later patch. > > > > Signed-off-by: Pierre Morel > > --- > > hw/s390x/s390-virtio-ccw.c | 42 ++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 42 insertions(+) > > > > diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c > > index e4b18aef49..899d3a4137 100644 > > --- a/hw/s390x/s390-virtio-ccw.c > > +++ b/hw/s390x/s390-virtio-ccw.c > > @@ -582,6 +582,47 @@ static ram_addr_t s390_fixup_ram_size(ram_addr_t sz) > > return newsz; > > } > > > > +/* > > + * In S390CCW machine we do not support threads for now, > > + * only sockets and cores. > > + */ > > +static void s390_smp_parse(MachineState *ms, QemuOpts *opts) > > It seems you based this on an older version of the code? The current > signature of this function since 1e63fe685804 ("machine: pass QAPI > struct to mc->smp_parse") is > > void (*smp_parse)(MachineState *ms, SMPConfiguration *config, Error **errp); > > That affects your parsing, and also lets you get rid of the ugly exit(1) > statements. > > > +{ > > + unsigned cpus = qemu_opt_get_number(opts, "cpus", 1); > > + unsigned sockets = qemu_opt_get_number(opts, "sockets", 1); > > + unsigned cores = qemu_opt_get_number(opts, "cores", 1); > > + > > + if (opts) { > > + if (cpus == 0 || sockets == 0 || cores == 0) { > > This behaviour looks different from what we do for other targets: if you > specify the value as 0, a value is calculated from the other values; > here, you error out. It's probably not a good idea to differ. I increasingly worry that we're making a mistake by going down the route of having custom smp_parse implementations per target, as this is showing signs of inconsistent behaviour and error reportings. I think the differences / restrictions have granularity at a different level that is being tested in many cases too. Whether threads != 1 is valid will likely vary depending on what CPU model is chosen, rather than what architecture is chosen. The same is true for dies != 1. We're not really checking this closely even in x86 - for example I can request nonsense such as a 25 year old i486 CPU model with hyperthreading and multiple dies qemu-system-x86_64 -cpu 486 -smp 16,cores=4,dies=2,threads=2 In this patch, there is no error reporting if the user specifies dies != 1 or threads != 1 - it just silently ignores the request which is not good. Some machine types may have constraints on CPU sockets. This can of course all be handled by custom smp_parse impls, but this is ultimately going to lead to alot of duplicated and inconsistent logic I fear. I wonder if we would be better off having machine class callback that can report topology constraints for the current configuration, along lines of smp_constraints(MachineState *ms, int *max_sockets, int *max_dies, int *max_cores, int *max_threads) And then have only a single smp_parse impl that takes into account these constraints, to report errors / fill in missing fields / etc ? 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 :|