Re: [libvirt] [RFC 12/42] pc: initialize legacy hotplug only for 2.6 and older machine types

On Thu, 12 May 2016 10:07:03 +0300 "Michael S. Tsirkin" <mst(a)redhat.com&gt; wrote: > On Wed, May 11, 2016 at 08:28:59PM -0300, Eduardo Habkost wrote: > > On Thu, May 12, 2016 at 12:51:55AM +0300, Michael S. Tsirkin wrote: > > > On Wed, May 11, 2016 at 03:50:39PM +0200, Igor Mammedov wrote: > > > > On Tue, 10 May 2016 17:24:14 -0300 > > > > Eduardo Habkost <ehabkost(a)redhat.com&gt; wrote: > > > > > > > > > On Mon, May 02, 2016 at 02:33:21PM +0200, Igor Mammedov wrote: > > > > > > on old machine types CPU hotplug was uncondtionally > > > > > > enabled since it was introduced, consuming IO ports > > > > > > and providing AML regardles of whether it was actually > > > > > > in use or not. Keep it so for 2.6 and older machines. > > > > > > > > > > > > New machine types will have an option to turn CPU > > > > > > hotplug on if it's needed while by default it stays > > > > > > disabled not consuming extra RAM/IO resources. > > > > > > > > > > > > Signed-off-by: Igor Mammedov <imammedo(a)redhat.com&gt; > > > > > > > > > > What if people are using "-machine pc -smp N,max_cpus=M"? > > > > > Shouldn't we at least warning about missing CPU hotplug support > > > > > when using just "max_cpus" with no "cpu-hotplug=on" with pc-2.7 > > > > > and newer? > > > > Yep, I'll add it on next respin. > > > > Would hard error better than warning? > > > > > > Most people don't need cpu hotplug, attempts > > > to hotplug fail, should be enough. > > > > People who don't need CPU hotplug shouldn't be using the max_cpus > > option. > > I agree. > > > I believe we should at least warn people (early, during > > initialization) that their configuration don't make sense > > anymore. > > I think we should try to keep old command line working > if we can. this patch won't break old command line for old machine types, but for new machine type users would need to fix it and be explicit if they want cpu-hotplug.