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

[Richard W.M. Jones]

On Fri, Sep 18, 2020 at 10:52:58AM +0100, Daniel P. Berrangé wrote:
> 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

I'm not using a new enough qemu to have that and it doesn't appear in
a released version, but I'll test again once we have a new enough
version.

> > 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.

I'll cap the number of CPUs in this patch.

Thanks,

Rich.

-- 
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