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From: David Hildenbrand <david@redhat.com>
To: "Alex Bennée" <alex.bennee@linaro.org>
Cc: qemu-devel@nongnu.org,
	Matthew Rosato <mjrosato@linux.vnet.ibm.com>,
	thuth@redhat.com, Eduardo Habkost <ehabkost@redhat.com>,
	cohuck@redhat.com,
	Richard Henderson <richard.henderson@linaro.org>,
	Alexander Graf <agraf@suse.de>,
	Markus Armbruster <armbru@redhat.com>,
	borntraeger@de.ibm.com, Igor Mammedov <imammedo@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [Qemu-devel] [PATCH v5 11/22] s390x: allow only 1 CPU with TCG
Date: Fri, 15 Sep 2017 15:36:15 +0200	[thread overview]
Message-ID: <7b5c88bf-50be-d692-2925-c549bfd79202@redhat.com> (raw)
In-Reply-To: <87vakk85k8.fsf@linaro.org>

On 15.09.2017 15:17, Alex Bennée wrote:
> 
> David Hildenbrand <david@redhat.com> writes:
> 
>> On 13.09.2017 18:13, Alex Bennée wrote:
>>>
>>> David Hildenbrand <david@redhat.com> writes:
>>>
>>>> Specifying more than 1 CPU (e.g. -smp 5) leads to SIGP errors (the
>>>> guest tries to bring these CPUs up but fails), because we don't support
>>>> multiple CPUs on s390x under TCG.
>>>>
>>>> Let's bail out if more than 1 is specified, so we don't raise people's
>>>> hope.
>>>
>>> Why does this restriction exist? Without MTTCG enabled -smp > 1 should
>>> be safe from any races.
>>
>> Because the actual SIGP code (instruction to start/stop ... CPUs) is not
>> implemented yet.
> 
> Ahh OK, I assume something like ARM's PCSI interface then.
> 
> When you do get around to implementing just ensure you use the async
> mechanism to initialise the target processor state to avoid races in
> MTTCG. Essentially you queue the work up on the target and then it is
> run before the powered up vCPU starts running code.

One step at a time, right now I only test with single threaded. MTTCG is
the next step. But I have a good feeling about mttcg, at least speaking
about the SIGP implementation (for the "critical" stuff - start, stop,
initialize - I reuse the KVM code which uses even sync work).

> 
> --
> Alex Bennée
> 


-- 

Thanks,

David

  reply	other threads:[~2017-09-15 13:36 UTC|newest]

Thread overview: 56+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-09-13 13:23 [Qemu-devel] [PATCH v5 00/22] s390x cleanups and CPU hotplug via device_add David Hildenbrand
2017-09-13 13:23 ` [Qemu-devel] [PATCH v5 01/22] exec, dump, i386, ppc, s390x: don't include exec/cpu-all.h explicitly David Hildenbrand
2017-09-13 13:23 ` [Qemu-devel] [PATCH v5 02/22] cpu: drop old comments describing members David Hildenbrand
2017-09-13 13:23 ` [Qemu-devel] [PATCH v5 03/22] s390x: get rid of s390-virtio.c David Hildenbrand
2017-09-13 16:34   ` David Hildenbrand
2017-09-13 16:54     ` Cornelia Huck
2017-09-13 13:23 ` [Qemu-devel] [PATCH v5 04/22] s390x: rename s390-virtio.h to s390-virtio-hcall.h David Hildenbrand
2017-09-13 13:24 ` [Qemu-devel] [PATCH v5 05/22] s390x: move s390_virtio_hypercall() " David Hildenbrand
2017-09-13 13:24 ` [Qemu-devel] [PATCH v5 06/22] s390x: move subsystem_reset() to s390-virtio-ccw.h David Hildenbrand
2017-09-13 13:24 ` [Qemu-devel] [PATCH v5 07/22] target/s390x: move some s390x typedefs to cpu-qom.h David Hildenbrand
2017-09-13 14:27   ` Thomas Huth
2017-09-13 14:44     ` David Hildenbrand
2017-09-13 15:04       ` Thomas Huth
2017-09-13 13:24 ` [Qemu-devel] [PATCH v5 08/22] s390x: move sclp_service_call() to sclp.h David Hildenbrand
2017-09-13 14:29   ` Thomas Huth
2017-09-13 14:42     ` David Hildenbrand
2017-09-13 15:21     ` Cornelia Huck
2017-09-13 15:23       ` David Hildenbrand
2017-09-13 13:24 ` [Qemu-devel] [PATCH v5 09/22] target/s390x: use trigger_pgm_exception() in s390_cpu_handle_mmu_fault() David Hildenbrand
2017-09-13 13:24 ` [Qemu-devel] [PATCH v5 10/22] target/s390x: use program_interrupt() in per_check_exception() David Hildenbrand
2017-09-13 13:24 ` [Qemu-devel] [PATCH v5 11/22] s390x: allow only 1 CPU with TCG David Hildenbrand
2017-09-13 14:06   ` Igor Mammedov
2017-09-13 16:13   ` Alex Bennée
2017-09-13 16:25     ` David Hildenbrand
2017-09-15 13:17       ` Alex Bennée
2017-09-15 13:36         ` David Hildenbrand [this message]
2017-09-13 13:24 ` [Qemu-devel] [PATCH v5 12/22] target/s390x: set cpu->id for linux user when realizing David Hildenbrand
2017-09-13 13:24 ` [Qemu-devel] [PATCH v5 13/22] target/s390x: use "core-id" for cpu number/address/id handling David Hildenbrand
2017-09-13 13:24 ` [Qemu-devel] [PATCH v5 14/22] target/s390x: rename next_cpu_id to next_core_id David Hildenbrand
2017-09-13 13:24 ` [Qemu-devel] [PATCH v5 15/22] s390x: print CPU definitions in sorted order David Hildenbrand
2017-09-13 13:24 ` [Qemu-devel] [PATCH v5 16/22] s390x: allow cpu hotplug via device_add David Hildenbrand
2017-09-28  6:01   ` Thomas Huth
2017-09-28 13:00     ` David Hildenbrand
2017-09-28 13:36     ` David Hildenbrand
2017-09-13 13:24 ` [Qemu-devel] [PATCH v5 17/22] s390x: CPU hot unplug via device_del cannot work for now David Hildenbrand
2017-09-13 15:45   ` Cornelia Huck
2017-09-13 13:24 ` [Qemu-devel] [PATCH v5 18/22] s390x: implement query-hotpluggable-cpus David Hildenbrand
2017-09-13 14:42   ` Igor Mammedov
2017-09-13 15:49   ` Cornelia Huck
2017-09-13 15:50     ` David Hildenbrand
2017-10-02  7:46   ` Markus Armbruster
2017-10-04  8:04     ` Cornelia Huck
2017-10-04 12:42       ` Markus Armbruster
2017-10-04 13:09         ` Cornelia Huck
2017-10-06 17:17           ` Markus Armbruster
2017-10-09 10:31             ` Marc-André Lureau
2017-09-13 13:24 ` [Qemu-devel] [PATCH v5 19/22] s390x: get rid of cpu_states and use possible_cpus instead David Hildenbrand
2017-09-13 14:45   ` Igor Mammedov
2017-09-13 13:24 ` [Qemu-devel] [PATCH v5 20/22] s390x: get rid of cpu_s390x_create() David Hildenbrand
2017-09-13 13:24 ` [Qemu-devel] [PATCH v5 21/22] s390x: generate sclp cpu information from possible_cpus David Hildenbrand
2017-09-13 13:24 ` [Qemu-devel] [PATCH v5 22/22] s390x: allow CPU hotplug in random core-id order David Hildenbrand
2017-09-13 14:46   ` Igor Mammedov
2017-09-13 16:58 ` [Qemu-devel] [PATCH v5 00/22] s390x cleanups and CPU hotplug via device_add Cornelia Huck
2017-10-02  7:47   ` Markus Armbruster
2017-10-04  8:05     ` Cornelia Huck
2017-10-20 15:45 ` David Hildenbrand

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