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Re: [Qemu-devel] [PATCH] sysemu: support up to 1024 vCPUs
From: |
Igor Mammedov |
Subject: |
Re: [Qemu-devel] [PATCH] sysemu: support up to 1024 vCPUs |
Date: |
Wed, 11 May 2016 16:20:08 +0200 |
On Wed, 11 May 2016 16:00:04 +0200
Greg Kurz <address@hidden> wrote:
> Some systems can already provide more than 255 hardware threads.
>
> Bumping the QEMU limit to 1024 seems reasonable:
> - it has no visible overhead in top
> - the limit itself has no effect on hot paths
>
> Signed-off-by: Greg Kurz <address@hidden>
> ---
>
> This was tested with a pseries guest only. I'd like to know if it is okay
> for other platforms.
#git grep MAX_CPUMASK_BITS
...
hw/arm/virt.c: mc->max_cpus = MAX_CPUMASK_BITS;
hw/ppc/spapr.c: mc->max_cpus = MAX_CPUMASK_BITS;
...
you probably don't want to change all those to 1024,
see/review a similar patch where I bump it upto 288 bits
https://lists.gnu.org/archive/html/qemu-devel/2016-05/msg01101.html
in addition where does 1024 come from?
is pseries capable to provide that many CPUs?
>
> include/sysemu/sysemu.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
> index 38fb3cad35e1..89d742caa477 100644
> --- a/include/sysemu/sysemu.h
> +++ b/include/sysemu/sysemu.h
> @@ -185,7 +185,7 @@ extern int mem_prealloc;
> *
> * Note that cpu->get_arch_id() may be larger than MAX_CPUMASK_BITS.
> */
> -#define MAX_CPUMASK_BITS 255
> +#define MAX_CPUMASK_BITS 1024
>
> #define MAX_OPTION_ROMS 16
> typedef struct QEMUOptionRom {
>