linux-kernel - Re: [Qemu-devel] [PATCH v4 11/15] target-s390x: New QMP command query-cpu-model

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Date:	Tue, 31 Mar 2015 15:28:26 -0300
From:	Eduardo Habkost <ehabkost@...hat.com>
To:	Michael Mueller <mimu@...ux.vnet.ibm.com>
Cc:	linux-s390@...r.kernel.org, kvm@...r.kernel.org,
	Gleb Natapov <gleb@...nel.org>, linux-kernel@...r.kernel.org,
	Alexander Graf <agraf@...e.de>, qemu-devel@...gnu.org,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Daniel Hansel <daniel.hansel@...ux.vnet.ibm.com>,
	"Jason J. Herne" <jjherne@...ux.vnet.ibm.com>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Andreas Faerber <afaerber@...e.de>,
	Richard Henderson <rth@...ddle.net>
Subject: Re: [Qemu-devel] [PATCH v4 11/15] target-s390x: New QMP command
 query-cpu-model

On Tue, Mar 31, 2015 at 01:21:05PM +0200, Michael Mueller wrote:
> On Mon, 30 Mar 2015 17:17:21 -0300
> Eduardo Habkost <ehabkost@...hat.com> wrote:
> 
> > On Mon, Mar 30, 2015 at 04:28:24PM +0200, Michael Mueller wrote:
> > > This patch implements a new QMP request named 'query-cpu-model'.
> > > It returns the cpu model of cpu 0 and its backing accelerator.
> > > 
> > > request:
> > >   {"execute" : "query-cpu-model" }
> > > 
> > > answer:
> > >   {"return" : {"name": "2827-ga2", "accel": "kvm" }}
> > 
> > If you are returning information about an existing CPU, why not just
> > extend the output of "query-cpus"?
> > 
> > (Existing qmp_query_cpus() calls cpu_synchronize_state(), which may be
> > undesired. But in this case we could add an optional parameter to
> > disable the return of data that requires stopping the VCPU).
> 
> Will the cpu_cpu_syncronize_state() really hurt in real life?
> query-cpus will be called only once a while...
> 

I was just thinking about possible reasons you wouldn't want to reuse
query-cpus, and thought cpu_synchronize_state() call could be one of
them.

> I will prepare the extension of query-cpus as an option but initially
> without the optional parameter.

I agree we can simply add the new info to query-cpus without any extra
parameter, and (if really necessary) we can worry about optimizing it by
avoiding the cpu_synchronize_state() call later.

-- 
Eduardo
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