On Mon, May 18, 2015 at 03:36:54PM -0300, Eduardo Habkost wrote:
> On Tue, May 12, 2015 at 11:06:25AM +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.
> >
> > 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>
>
> Looks good to me, minor comments below:
>
> > ---
> > exec.c | 55
> > ++++++++++++++++++++++++++++++++++++++++++++++++++-----
> > include/qom/cpu.h | 1 +
> > qom/cpu.c | 7 +++++++
> > 3 files changed, 58 insertions(+), 5 deletions(-)
> >
> > diff --git a/exec.c b/exec.c
> > index 5cf821e..c8c4e53 100644
> > --- a/exec.c
> > +++ b/exec.c
> > @@ -518,21 +518,66 @@ 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 -1;
> > + } else {
> > + bitmap_set(cpu_index_map, cpu, 1);
> > + return cpu;
> > + }
>
> I prefer the following style, to avoid indenting the non-error path:
>
> if (error_condition) {
> error_setg(...);
> return;
> }
>
> bitmap_set(...)
> return cpu;
>
> (Which is exactly the style you used in cpu_exec_exit() below, by the
> way).
Sure, I can change this in next post.
>
> > +}
> > +
> > +void cpu_exec_exit(CPUState *cpu)
> > +{
> > + if (cpu->cpu_index == -1) {
> > + /* cpu_index was never allocated by this @cpu or was already
> > freed. */
> > + return;
> > + }
> > +
> > + bitmap_clear(cpu_index_map, cpu->cpu_index, 1);
> > + cpu->cpu_index = -1;
> > +}
> > +#else
> > +
> > +static int cpu_get_free_index(Error **errp)
> > +{
> > + CPUState *some_cpu;
> > + int cpu_index = 0;
> > +
> > + CPU_FOREACH(some_cpu) {
> > + cpu_index++;
> > + }
> > + return cpu_index;
> > +}
> > +
> > +void cpu_exec_exit(CPUState *cpu)
> > +{
> > +}
> > +#endif
> > +
> > void cpu_exec_init(CPUArchState *env, Error **errp)
> > {
> > CPUState *cpu = ENV_GET_CPU(env);
> > CPUClass *cc = CPU_GET_CLASS(cpu);
> > - CPUState *some_cpu;
> > int cpu_index;
> > + Error *local_err = NULL;
> >
> > #if defined(CONFIG_USER_ONLY)
> > cpu_list_lock();
> > #endif
> > - cpu_index = 0;
> > - CPU_FOREACH(some_cpu) {
> > - cpu_index++;
> > + cpu_index = cpu->cpu_index = cpu_get_free_index(&local_err);
> > + if (local_err) {
> > + error_propagate(errp, local_err);
> > + return;
> > }
> > - cpu->cpu_index = cpu_index;
> > cpu->numa_node = 0;
> > QTAILQ_INIT(&cpu->breakpoints);
> > QTAILQ_INIT(&cpu->watchpoints);
> > diff --git a/include/qom/cpu.h b/include/qom/cpu.h
> > index 39f0f19..7db310e 100644
> > --- a/include/qom/cpu.h
> > +++ b/include/qom/cpu.h
> > @@ -672,6 +672,7 @@ void cpu_watchpoint_remove_all(CPUState *cpu, int mask);
> >
> > void QEMU_NORETURN cpu_abort(CPUState *cpu, const char *fmt, ...)
> > GCC_FMT_ATTR(2, 3);
> > +void cpu_exec_exit(CPUState *cpu);
>
> Why don't we keep both cpu_exec_init() and cpu_exec_exit() in the same
> header file?
Currently cpu_exec_init() is in exec-all.h.
1. If I put cpu_exec_exit() also there, qom/cpu.c doesn't like it since
many definitions (like ram_addr_t etc) aren't known in qom/cpu.c.
2. I can't move cpu_exec_init() declaration to qom/cpu.h since it results
in the use of poisoned definition of CPUArchState from qom/cpu.c
Hence I separated them into different hearder files.
Regards,
Bharata.
