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Re: [Qemu-ppc] [Qemu-devel] [PATCH 2/2] vl: Print CPU help after we've r

From: Thomas Huth
Subject: Re: [Qemu-ppc] [Qemu-devel] [PATCH 2/2] vl: Print CPU help after we've registered the CPU accelerators
Date: Tue, 7 Mar 2017 10:02:26 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.7.0

On 03.03.2017 15:58, Eduardo Habkost wrote:
> I am not convinced that the output of "-cpu help" and
> "-cpu help -machine accel=kvm" should look different. Do you have
> an example of what exactly is wrong with the output currently?

The problem is that on POWER, we've got a "family" of CPUs with
different sub-types, e.g. for POWER8:

$ qemu-system-ppc64 -cpu ? | grep POWER8
PowerPC POWER8E_v2.1     PVR 004b0201
PowerPC POWER8E          (alias for POWER8E_v2.1)
PowerPC POWER8NVL_v1.0   PVR 004c0100
PowerPC POWER8NVL        (alias for POWER8NVL_v1.0)
PowerPC POWER8_v2.0      PVR 004d0200
PowerPC POWER8           (alias for POWER8_v2.0)

Most of the users don't know about the current subtype that they are
using, and just want to use "-cpu POWER8" - and for example we've also
got an agreement with the libvirt folks that they can always use "-cpu
POWER8" for any kind of POWER8 system, no matter whether the host is
using a POWER8E or POWER8NVL chip.
So the "POWER8" alias now gets updated internally in QEMU to the correct
host CPU type ... but the output of "-cpu help" is then still wrong.
I agree that it's kind of ugly to have different help texts depending on
whether "accel=kvm" has been used or not, but that sounds still better
to me than printing wrong information here.
Thinking about this again ... maybe it would be better if we'd rework
the help text to print out something like this instead:

PowerPC POWER8           (alias for any POWER8 chip)

... so that we simply get rid of the version/subtype information here


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