Re: [Qemu-devel] [PULL v2 05/22] cpu: Convert cpu_index into a bitmap

[Andreas Färber]

Am 07.07.2015 um 19:16 schrieb Andreas Färber:
> From: Bharata B Rao <address@hidden>
> 
> 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 <address@hidden>
> Reviewed-by: Eduardo Habkost <address@hidden>
> Reviewed-by: Igor Mammedov <address@hidden>
> Reviewed-by: David Gibson <address@hidden>
> Reviewed-by: Peter Crosthwaite <address@hidden>
> Acked-by: Paolo Bonzini <address@hidden>
> Signed-off-by: Peter Crosthwaite <address@hidden>
> [AF: max_cpus -> MAX_CPUMASK_BITS]
> Signed-off-by: Andreas Färber <address@hidden>
> ---
>  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 8abac69..02602b6 100644
> --- a/exec.c
> +++ b/exec.c
[...]
> @@ -542,11 +587,11 @@ void cpu_exec_init(CPUArchState *env, Error **errp)
>  #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);

This is lacking a matching cpu_list_unlock() in the CONFIG_USER_ONLY case:

diff --git a/exec.c b/exec.c
index ee5bf7c..d817e5f 100644
--- a/exec.c
+++ b/exec.c
@@ -590,6 +590,9 @@ void cpu_exec_init(CPUArchState *env, Error **errp)
     cpu_index = cpu->cpu_index = cpu_get_free_index(&local_err);
     if (local_err) {
         error_propagate(errp, local_err);
+#if defined(CONFIG_USER_ONLY)
+        cpu_list_unlock();
+#endif
         return;
     }
     QTAILQ_INSERT_TAIL(&cpus, cpu, node);

Regards,
Andreas

> +        return;
>      }
> -    cpu->cpu_index = cpu_index;
>      QTAILQ_INSERT_TAIL(&cpus, cpu, node);
>  #if defined(CONFIG_USER_ONLY)
>      cpu_list_unlock();
[snip]

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