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

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.