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Re: [PATCH 3/4] hw/i386: add facility to expose CPU topology over fw-cfg
From: |
Laszlo Ersek |
Subject: |
Re: [PATCH 3/4] hw/i386: add facility to expose CPU topology over fw-cfg |
Date: |
Thu, 10 Oct 2019 18:15:21 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 |
On 10/10/19 12:01, Michael S. Tsirkin wrote:
> On Tue, Oct 08, 2019 at 05:59:31PM +0200, Igor Mammedov wrote:
>> So far there were no need for it as all possible cpus are
>> described in ACPI tables passed to guest, but I'm not going
>> to suggest to parse them on firmware side as it's too complicated :)
>
> We can always add a QEMU specific data table by the way.
> Format would be up to us and would be easy to parse.
> I don't see a big advantage as compared to fw cfg though.
I'd like to comment just on this part.
*If* we decide to expose the information through some kind of data table
(as opposed to the modern CPU hotplug register block), then the
representation *must* be a dedicated fw_cfg blob. It cannot be an ACPI
table.
The reason is that *selecting* the fw_cfg blob that contains the ACPI
linker/loader script is a very specific action (it re-generates the ACPI
payload, with dependencies on assigned PCI resources). Therefore, it is
done in a super-particular spot in the firmware.
On the other hand, the "possible CPUs count" is needed much earlier than
that. I need to fetch that info way before PCI resource assignment
appears on the radar.
So please let us stick with "ACPI is only for the guest OS to read" rule
-- it's not only a parsing convenience for the firmware, but a real
necessity.
Thanks
Laszlo
- Re: [PATCH 3/4] hw/i386: add facility to expose CPU topology over fw-cfg, (continued)
- Re: [PATCH 3/4] hw/i386: add facility to expose CPU topology over fw-cfg, Igor Mammedov, 2019/10/08
- Re: [PATCH 3/4] hw/i386: add facility to expose CPU topology over fw-cfg, Michael S. Tsirkin, 2019/10/10
- Re: [PATCH 3/4] hw/i386: add facility to expose CPU topology over fw-cfg, Igor Mammedov, 2019/10/10
- Re: [PATCH 3/4] hw/i386: add facility to expose CPU topology over fw-cfg, Laszlo Ersek, 2019/10/10
- Re: [PATCH 3/4] hw/i386: add facility to expose CPU topology over fw-cfg, Michael S. Tsirkin, 2019/10/10
- Re: [PATCH 3/4] hw/i386: add facility to expose CPU topology over fw-cfg, Laszlo Ersek, 2019/10/11
- Re: [PATCH 3/4] hw/i386: add facility to expose CPU topology over fw-cfg, Laszlo Ersek, 2019/10/11
- Re: [PATCH 3/4] hw/i386: add facility to expose CPU topology over fw-cfg,
Laszlo Ersek <=
Re: [PATCH 3/4] hw/i386: add facility to expose CPU topology over fw-cfg, Laszlo Ersek, 2019/10/08
Re: [PATCH 3/4] hw/i386: add facility to expose CPU topology over fw-cfg, Eduardo Habkost, 2019/10/09
[PATCH 4/4] hw/i386/pc: expose CPU topology over fw-cfg, Laszlo Ersek, 2019/10/08
Re: [PATCH 0/4] hw/i386: pass "MachineState.smp.max_cpus" to OVMF, no-reply, 2019/10/08