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From: | Paolo Bonzini |
Subject: | Re: [PATCH] hostmem: default the amount of prealloc-threads to smp-cpus |
Date: | Wed, 18 May 2022 16:06:47 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 |
On 5/18/22 15:31, Daniel P. Berrangé wrote:
When picking defaults there is never a perfect answer, it is more a matter of the least-worst option. It is pretty clear that nthreads=1 is terrible for any large VMs. Defaulting it to nvcpus made conceptual sense as the user has implicit said that they expect the VM to be able to consume nvcpus worth of CPU time on the host, so we might as well consume that allotted resource.
I agree. Yes, one could argue that the regression was on the libvirt side, but it's easier to fix it in QEMU.
If we later add the ability to create a memory backend before machine creation (for example with a QMP-only binary), then it's of course okay for those backends to use only one thread and require a manual choice for the # or preallocation threads.
Paolo
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