Re: [PATCH v2 1/1] qemu: Add support for RAPL MSRs feature
Daniel P. Berrangé, Sep 03, 2024 at 12:08:
On Mon, Sep 02, 2024 at 03:09:42PM +0200, Peter Krempa wrote:
> On Thu, Aug 22, 2024 at 17:59:47 +0200, Anthony Harivel wrote:
> > Add the support in libvirt to activate the RAPL feature in QEMU.
> I suppose that the 'rapl-helper-socket' is a shared (multiple qemu's
use
> it) resource set up beforehand by the admin. Right?
The qemu-pr-helper could be run as a single instnce, or it could be
run per-QEMU instance. The latter would give us better security
isolation, for what is a privileged daemon. On the other hand, I
wonder about the CPU overhead of having 100's of copies of the
process running on a host.
If it runs on a single instance, then the socket needs to be chmod/chown
to something like qemu / libvirt group with access only to root and
group.
Running one helper instance per-QEMU instance would mean that every
instance read 1 MSR / Package every second. The socket is left open
(thanks to Daniel suggestion in QEMU review). The impact would be quite
low I guess on the housekeeping CPU.
When I designed the daemon with Paolo, the first solution was the main
idea but I'm open to any solution that leads to a better adoption of the
feature.
Thanks,
Anthony
> If that is the case that means the lifecycle of the daemon and
> permissions (including selinux) for accessing the socket are not
> something that libvirt needs to deal with.
>
> If either of them isn't true please outline how that socket is to be
> used to see how libvirt will need to approach it.
>
With regards,
Daniel
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