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Re: X86: Abnormal variation in Freebsd VM launch time w.r.t freebsd gues

From: Daniel P . Berrangé
Subject: Re: X86: Abnormal variation in Freebsd VM launch time w.r.t freebsd guest config
Date: Tue, 7 Apr 2020 10:22:46 +0100
User-agent: Mutt/1.13.3 (2020-01-12)

On Tue, Apr 07, 2020 at 09:59:59AM +0530, gokul cg wrote:
> Hi Team,
> We are observing abnormal variation in VM launch time w.r.t guest config.
> A simple VM(2gb ram no passthrough device) creation takes usually 6sec
> (Time from execution of 'virsh create guest.xml  to get print "Welcome to
> FreeBSD"' ),but when we add a USB passthrough device launch time increased
> to 18-19 sec and further increased to 39-44sec when we have increased guest
> ram to 48Gb.


> Note : 1) This we have seen with legacy pci passthrough device not with
> vfio. And we have not noticed any perfoance impact other than qemu-init/vm
> laucn time .

Legacy pci passthrough support was deleted way back to 2017, and we had
deprecated it for 2 years before then, in favour of VFIO.

>  Any suggestions to improve launch time with legacy passthrough ?

Just stop using legacy PCI assignment. VFIO has been the recommended
impl for 5+ years now.

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