Re: [Xen-devel] [PATCH] xen/domctl: lower loglevel of XEN_DOMCTL_memory_mapping

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 10.09.15 at 07:28, <tiejun.chen@xxxxxxxxx> wrote:
>> > If the 64 limit was arbitrary then I would suggest increasing it to at 
>> > least
>>> 1024 so that
>>> at least 4M of BAR can be mapped in one go and it reduces the overhead by a
>>> factor of 16.
>>
>> 1024 may be a little much, but 256 is certainly a possibility, plus
>> Konrad's suggestion to allow this limit to be controlled via command
>> line option.
> 
> Are you guys talking this way?

Sort of (the patch has the intended effect, but for its size very
many rough edges).

Jan

> diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
> index 3946e4c..a9671bb 100644
> --- a/xen/arch/x86/setup.c
> +++ b/xen/arch/x86/setup.c
> @@ -88,6 +88,10 @@ boolean_param("noapic", skip_ioapic_setup);
>   s8 __read_mostly xen_cpuidle = -1;
>   boolean_param("cpuidle", xen_cpuidle);
> 
> +/* once_mapping_mfns: memory mapping mfn bumbers once. */
> +unsigned int xen_once_mapping_mfns;
> +integer_param("once_mapping_mfns", xen_once_mapping_mfns);
> +
>   #ifndef NDEBUG
>   unsigned long __initdata highmem_start;
>   size_param("highmem-start", highmem_start);
> diff --git a/xen/common/domctl.c b/xen/common/domctl.c
> index 3bf39f1..82c85e3 100644
> --- a/xen/common/domctl.c
> +++ b/xen/common/domctl.c
> @@ -33,6 +33,8 @@
>   #include <public/domctl.h>
>   #include <xsm/xsm.h>
> 
> +extern unsigned int xen_once_mapping_mfns;
> +
>   static DEFINE_SPINLOCK(domctl_lock);
>   DEFINE_SPINLOCK(vcpu_alloc_lock);
> 
> @@ -1035,7 +1037,7 @@ long 
> do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
> 
>           ret = -E2BIG;
>           /* Must break hypercall up as this could take a while. */
> -        if ( nr_mfns > 64 )
> +        if ( nr_mfns > xen_once_mapping_mfns )
>               break;
> 
>           ret = -EPERM;
> 
> Thanks
> Tiejun




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