<div class='zcontentRow' > Hi Jirka,<br/><br/>Thanks for your reviewing. But in the condition I described, libvirt has no chance to translate into a different model, because it has failed in the virCPUCompare before translate and the start of the domain will report the error, it that correct? <br/>For example, a host lacks "monitor" feature, which means that we can't see "monitor" flag when we run "cat /proc/cpuinfo", it will report error when we try to start the domain with core2duo model:<br/>"error: the CPU is incompatible with host CPU: Host CPU does not provide<br/>required features: monitor"<br/><br/><br/>Yi Wang <br/> <div class="zhistoryRow"><div class="zhistoryDes" style="width: 100%; height: 28px; line-height: 28px; background-color: #E0E5E9; color: #1388FF; text-align: center;" language-data="HistoryOrgTxt">Original<i class="fa fa-angle-down zwriteToggleBtn"></i> </div> <div id="zwriteHistoryContainer"> <div class="control-group zhistoryPanel"> <p class="zhistoryContent"><div style="background-color: rgb(245, 246, 248);"><strong language-data="HistorySenderTxt">Sender:</strong><span class="zreadUserName">JiriDenemark</span></div><div style="background-color: rgb(245, 246, 248);"><strong language-data="HistoryTOTxt">To:</strong><span class="zreadUserName" style="display: inline-block;">WangYi10129963;</span></div><div style="background-color: rgb(245, 246, 248);"><strong language-data="HistoryCCTxt">Cc:</strong><span class="zreadUserName" style="display: inline-block;">libvir-list@redhat.com;</span><span class="zreadUserName" style="display: inline-block;">LiuJianJun10033482;</span></div><div style="background-color: rgb(245, 246, 248);"><strong language-data="HistoryDateTxt" >Date:</strong><span class=>2017-06-07 01:56:02</span></div><div style="background-color: rgb(245, 246, 248);"><strong language-data="HistorySubjectTxt">Subject:</strong><span class="zreadTitle"><strong>Re: [libvirt] [PATCH] qemu: Starting a domain with custom model andallowed-fallback failed when host lacks some CPU features</strong></span></div><html><body><div style="width:100.00%; padding-left:8px; padding-right:8px;"><br/> On Tue, Jun 06, 2017 at 12:23:01 -0400, Yi Wang wrote:<br />> An attemp to start a domain requesting a custom CPU model, core2duo, for<br />> example, will fail if some feature that the model needs doesn't exist in that<br />> host, even though fallback attibute is set allow:<br />> "error: the CPU is incompatible with host CPU: Host CPU does not provide<br />> required features: monitor"<br />> Of course we can start that domain through forbidding that feature, but<br />> that may not be flexible.<br /><br />NACK, it works exactly as designed. The fallback attribute would make a<br />difference only if core2duo CPU model was not supported by QEMU, then<br />libvirt would translate it into a different supported one.<br /><br />Jirka<br /> </div></body></html></p> </div> </div></div> </div>