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Re: [Qemu-ppc] [RFC PATCH v2 14/23] cpus: Convert cpu_index into a bitma
From: |
Bharata B Rao |
Subject: |
Re: [Qemu-ppc] [RFC PATCH v2 14/23] cpus: Convert cpu_index into a bitmap |
Date: |
Wed, 25 Mar 2015 14:22:08 +0530 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Wed, Mar 25, 2015 at 02:23:29PM +1100, David Gibson wrote:
> On Mon, Mar 23, 2015 at 07:05:55PM +0530, Bharata B Rao wrote:
> > 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.
> >
> > Signed-off-by: Bharata B Rao <address@hidden>
> > ---
> > exec.c | 37 ++++++++++++++++++++++++++++++++++---
> > include/qom/cpu.h | 8 ++++++++
> > 2 files changed, 42 insertions(+), 3 deletions(-)
> >
> > diff --git a/exec.c b/exec.c
> > index e1ff6b0..9bbab02 100644
> > --- a/exec.c
> > +++ b/exec.c
> > @@ -527,21 +527,52 @@ 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_cpus);
> > +
> > + if (cpu == max_cpus) {
> > + error_setg(errp, "Trying to use more CPUs than allowed max of
> > %d\n",
> > + max_cpus);
> > + return max_cpus;
> > + } else {
> > + bitmap_set(cpu_index_map, cpu, 1);
> > + return cpu;
> > + }
> > +}
> > +
> > +void cpu_exec_exit(CPUState *cpu)
> > +{
> > + bitmap_clear(cpu_index_map, cpu->cpu_index, 1);
> > +}
>
> AFAICT, this function is never called, which seems like a bug.
It is called in subsequent patch. If you are suggesting that a function
shouldn't be defined in a patch where it not used, I can move this
down to the other patch.
Regards,
Bharata.
- Re: [Qemu-ppc] [RFC PATCH v2 11/23] ppc: Create sockets and cores for CPUs, (continued)
[Qemu-ppc] [RFC PATCH v2 12/23] spapr: CPU hotplug support, Bharata B Rao, 2015/03/23
[Qemu-ppc] [RFC PATCH v2 13/23] cpus: Add Error argument to cpu_exec_init(), Bharata B Rao, 2015/03/23
[Qemu-ppc] [RFC PATCH v2 14/23] cpus: Convert cpu_index into a bitmap, Bharata B Rao, 2015/03/23
[Qemu-ppc] [RFC PATCH v2 16/23] cpus: Reclaim vCPU objects, Bharata B Rao, 2015/03/23
[Qemu-ppc] [RFC PATCH v2 15/23] ppc: Move cpu_exec_init() call to realize function, Bharata B Rao, 2015/03/23
[Qemu-ppc] [RFC PATCH v2 17/23] xics_kvm: Don't enable KVM_CAP_IRQ_XICS if already enabled, Bharata B Rao, 2015/03/23
[Qemu-ppc] [RFC PATCH v2 18/23] xics_kvm: Add cpu_destroy method to XICS, Bharata B Rao, 2015/03/23