Re: [Xen-devel] [PATCH] arm/domain: allocate pages according to the order of struct domain size

[Julien Grall <julien.grall@xxxxxxx>]

Hello Jiandi,

On 08/06/2016 07:54, Jiandi An wrote:
> As the number of CPUs supported on the system grows, number of
> GIC redistributors and mmio handlers increase.  We need to increase
> MAX_RDIST_COUNT and MAX_IO_HANDLER which makes size of struct domain
> bigger than one page.
With this change, the memory footprint of a domain will increase by 4KB 
even if they don't use GICv3.
What is the size of the domain structure with your patch?

I would much prefer to allocate separate memory for the vGIC 
redistributors if it takes too much space.
> Remove the BUILD_BUG_ON check for if size of struct domain is greater
> than PAGE_SIZE.  And allocate xenheap pages according to the order of
> the size of struct domain.
>
> Signed-off-by: Jiandi An <anjiandi@xxxxxxxxxxxxxx>
> ---
>  xen/arch/arm/domain.c      | 5 +++--
>  xen/include/asm-arm/gic.h  | 2 +-
>  xen/include/asm-arm/mmio.h | 2 +-
>  3 files changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c
> index 1365b4a..7f69236 100644
> --- a/xen/arch/arm/domain.c
> +++ b/xen/arch/arm/domain.c
> @@ -438,8 +438,9 @@ void startup_cpu_idle_loop(void)
>  struct domain *alloc_domain_struct(void)
>  {
>      struct domain *d;
> -    BUILD_BUG_ON(sizeof(*d) > PAGE_SIZE);
> -    d = alloc_xenheap_pages(0, 0);
> +    unsigned int order = get_order_from_bytes(sizeof(*d));
> +
> +    d = alloc_xenheap_pages(order, 0);
>      if ( d == NULL )
>          return NULL;
>
> diff --git a/xen/include/asm-arm/gic.h b/xen/include/asm-arm/gic.h
> index cd97bb2..8165de6 100644
> --- a/xen/include/asm-arm/gic.h
> +++ b/xen/include/asm-arm/gic.h
> @@ -20,7 +20,7 @@
>
>  #define NR_GIC_LOCAL_IRQS  NR_LOCAL_IRQS
>  #define NR_GIC_SGI         16
> -#define MAX_RDIST_COUNT    4
> +#define MAX_RDIST_COUNT    64
How many re-distributor regions does your platform have?

>  #define GICD_CTLR       (0x000)
>  #define GICD_TYPER      (0x004)
> diff --git a/xen/include/asm-arm/mmio.h b/xen/include/asm-arm/mmio.h
> index da1cc2e..798d373 100644
> --- a/xen/include/asm-arm/mmio.h
> +++ b/xen/include/asm-arm/mmio.h
> @@ -23,7 +23,7 @@
>  #include <asm/processor.h>
>  #include <asm/regs.h>
>
> -#define MAX_IO_HANDLER  16
> +#define MAX_IO_HANDLER  32
The vGICv3 driver is allocating one I/O handler per redistributor 
region. So if you bump MAX_RDIST_COUNT to 64, you at least need to bump 
MAX_IO_HANDLER to 80.
However, I am bit concerned of the performance impact in long-term 
because the lookup is linear.
Regards,

--
Julien Grall

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