On Wed, 15 Jul 2015 09:12:48 +0530 Bharata B Rao <bharata....@gmail.com> wrote:
> On Tue, Jul 14, 2015 at 5:17 PM, Igor Mammedov <imamm...@redhat.com> > wrote: > > On Tue, 14 Jul 2015 16:08:54 +0530 > > Bharata B Rao <bhar...@linux.vnet.ibm.com> wrote: > > > >> On Thu, Jul 09, 2015 at 03:23:55PM +0200, Andreas Färber wrote: > >> > From: Bharata B Rao <bhar...@linux.vnet.ibm.com> > >> > > >> > Currently CPUState::cpu_index is monotonically increasing and a > >> > newly created CPU always gets the next higher index. The next > >> > available index is calculated by counting the existing number of > >> > CPUs. This is fine as long as we only add CPUs, but there are > >> > architectures which are starting to support CPU removal, too. > >> > For an architecture like PowerPC which derives its CPU > >> > identifier (device tree ID) from cpu_index, the existing logic > >> > of generating cpu_index values causes problems. > >> > > >> > With the currently proposed method of handling vCPU removal by > >> > parking the vCPU fd in QEMU > >> > (Ref: > >> > http://lists.gnu.org/archive/html/qemu-devel/2015-02/msg02604.html), > >> > generating cpu_index this way will not work for PowerPC. > >> > > >> > This patch changes the way cpu_index is handed out by maintaining > >> > a bit map of the CPUs that tracks both addition and removal of > >> > CPUs. > >> > > >> > The CPU bitmap allocation logic is part of cpu_exec_init(), > >> > which is called by instance_init routines of various CPU > >> > targets. Newly added cpu_exec_exit() API handles the > >> > deallocation part and this routine is called from generic CPU > >> > instance_finalize. > >> > > >> > Note: This new CPU enumeration is for !CONFIG_USER_ONLY only. > >> > CONFIG_USER_ONLY continues to have the old enumeration logic. > >> > > >> > Signed-off-by: Bharata B Rao <bhar...@linux.vnet.ibm.com> > >> > Reviewed-by: Eduardo Habkost <ehabk...@redhat.com> > >> > Reviewed-by: Igor Mammedov <imamm...@redhat.com> > >> > Reviewed-by: David Gibson <da...@gibson.dropbear.id.au> > >> > Reviewed-by: Peter Crosthwaite <peter.crosthwa...@xilinx.com> > >> > Acked-by: Paolo Bonzini <pbonz...@redhat.com> > >> > Signed-off-by: Peter Crosthwaite <crosthwaite.pe...@gmail.com> > >> > [AF: max_cpus -> MAX_CPUMASK_BITS] > >> > Signed-off-by: Andreas Färber <afaer...@suse.de> > >> > --- > >> > exec.c | 58 > >> > ++++++++++++++++++++++++++++++++++++++++++++++++++----- > >> > include/qom/cpu.h | 1 + qom/cpu.c | 7 +++++++ > >> > 3 files changed, 61 insertions(+), 5 deletions(-) > >> > > >> > diff --git a/exec.c b/exec.c > >> > index ce5fadd..d817e5f 100644 > >> > --- a/exec.c > >> > +++ b/exec.c > >> > @@ -526,12 +526,57 @@ void tcg_cpu_address_space_init(CPUState > >> > *cpu, AddressSpace *as) } > >> > #endif > >> > > >> > +#ifndef CONFIG_USER_ONLY > >> > +static DECLARE_BITMAP(cpu_index_map, MAX_CPUMASK_BITS); > >> > + > >> > +static int cpu_get_free_index(Error **errp) > >> > +{ > >> > + int cpu = find_first_zero_bit(cpu_index_map, > >> > MAX_CPUMASK_BITS); + > >> > + if (cpu >= MAX_CPUMASK_BITS) { > >> > + error_setg(errp, "Trying to use more CPUs than max of > >> > %d", > >> > + MAX_CPUMASK_BITS); > >> > + return -1; > >> > + } > >> > >> If this routine and hence cpu_exec_init() (which is called from > >> realize routine) don't error out when max_cpus is reached, archs > >> supporting CPU hotplug using device_add will find it difficult to > >> fail the realization of CPU when hotplugging of more than max_cpus > >> is attempted. > >> > >> An alternative is to explicitly check for the returned cpu_index > >> in realize call within each arch and fail if the cpu_index obtained > >> is greater than max_cpus. So for ppc, I could put such a check in > >> target-ppc/translate_init:ppc_cpu_realizefn(), but > >> ppc_cpu_realizefn() is a common routine for all targets under ppc > >> and some targets like ppc64abi32-linux-user don't have visibility > >> to max_cpus which is in vl.c. > >> > >> Any thoughts on the above problem ? > > we already have MachineClass.max_cpus which is max > > supported limit of machine type. > > Perhaps make max_cpus a property of MashineState > > MachineClass.max_cpus is the maximum number of CPUs supported for the > machine. What we want to check here is against the max_cpus that the > guest has booted with. > > So are you suggesting that we move vl.c:max_cpus to > MachineState.max_cpus and use that from all archs instead of using > vl.c:max_cpus directly ? yep, along the way move related cpus,threads,sockets,cores from vl.c to MachineState > > Regards, > Bharata.