Date: Fri, 28 Sep 2018 09:30:56 -0700 (PDT) From: "Rodney W. Grimes" <freebsd-rwg@pdx.rh.CN85.dnsmgr.net> To: Jakub Chromy <hicks@cgi.cz> Cc: "freebsd-virtua." <freebsd-virtualization@freebsd.org> Subject: Re: New bhyve user Message-ID: <201809281630.w8SGUuB4078064@pdx.rh.CN85.dnsmgr.net> In-Reply-To: <60055d7f-c378-7242-5bd5-7f5b60779b61@cgi.cz>
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> > > > ?So if one guest launch a lot of cpu hungry thread it could "starve" > > the others guests with less thread usgin cpu time. > > As far as what I heard here on this forum, you should NOT overcommit the > vCPUs. You seemed to have heard incorrectly. There is little to no issues overcommiting CPU's in bhyve, I have a 2 core, 4 thread system with 6 VM's, each vm using 1 vCPU, this is a 50% overcommit and it my base line load. I frequently fire up 2 and 4 core VM's to do real work without any issues. Now, you do NOT want to end up in situation where these VM's are over loading the actually avaliable CPU cycles, what I am doing works becasue my base line 6 VM's only actually consume about 1.5 cpus, so I actually do have 2.5 sitting idle. What does NOT work well is overcommiting Memory, that kinda puts you in a real bad state. I also stronly recommend using -S (wire memory) option, this insures you actually can hard allocate any memory that a VM needs. > > When you keep the number of vCPUs assigned to your vms lower than > physical CPUs (= hyperthreaded cores), you should be fine. It is all a mater of Load, as long as your host load stays below the number of CPU threads you actually have things in this aspect tend to work just fine. And if you do exceed this everyone slows down in a fairly fair fashion. -- Rod Grimes rgrimes@freebsd.org
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