[Libguestfs] [PATCH v2v] v2v: Set the number of vCPUs to same as host number of pCPUs.

[Daniel P. Berrangé]

On Fri, Sep 18, 2020 at 10:44:03AM +0100, Richard W.M. Jones wrote:
> So it didn't make any noticable difference in my test.  I wonder if
> the test guest I'm using (Fedora 32 using dracut) doesn't use parallel
> compression?

Do you do anything special to optimize storage ? If the thing using
parallel CPUs in the guest is doing I/O you'd likely want to tune
storage at same time. In current QEMU git master there's a change[1]
that sets  viort-blk/virtio-scsi  num_queues to match SMP count,
so the guest OS get fully parallel I/O from meach guest CPU.

[1] a4eef0711b2cf7a7476c3e2c202a414b68a1baa0

> However I don't think it can cause a problem and it seems obvious that
> it could benefit some cases.

What's the default RAM size ?  On hosts with very large numbers of CPUs
(100's) you might need to scale up RAM size too so you keep a sane
RAM-per-CPU ratio.  Or default to host CPUs, but cap it at say 32.


Regards,
Daniel
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