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Re: Qemu storage performance drops when smp > 1 (NetBSD 9.3 + Qemu/nvmm + ZVOL)



Hello Brian,

On 18.08.22 07:10, Brian Buhrow wrote:
	hello.  that's interesting.  Do the cores used for the vms also get used for the host os?
Can you arrange things so that the host os gets dedicated cores that the vms can't use?  If you
do that, do you still see a performance drop when you add cores to the vms?

the host OS has no other purpose than managing the VMs at this time. So apart from the minimal footprint of the hosts processes (postfix, syslog...) all the ressources are available to the Qemu processes.

In the meantime, because of the other mail in this thread, I believe my fundamental misunderstanding is/was that I can overcommit a physical 2 Core CPU with a multiple of virtual cores without penalties. I'm starting to see that now, I wasn't aware that the context switches are so expensive that they can paralyze the whole I/O system.

Kind regards
Matthias

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