svn commit: r242029 - head/sys/kern

[Garrett Cooper]

On Wed, Oct 24, 2012 at 6:46 PM, Alfred Perlstein <alfred at freebsd.org> wrote:
> Author: alfred
> Date: Thu Oct 25 01:46:20 2012
> New Revision: 242029
> URL: http://svn.freebsd.org/changeset/base/242029
>
> Log:
>   Allow autotune maxusers > 384 on 64 bit machines
>
>   A default install on large memory machines with multiple 10gigE interfaces
>   were not being given enough mbufs to do full bandwidth TCP or NFS traffic.
>
>   To keep the value somewhat reasonable, we scale back the number of
>   maxuers by 1/6 past the 384 point.  This gives us enough mbufs for most
>   of our pretty basic 10gigE line-speed tests to complete.
>
> Modified:
>   head/sys/kern/subr_param.c
>
> Modified: head/sys/kern/subr_param.c
> ==============================================================================
> --- head/sys/kern/subr_param.c  Thu Oct 25 01:27:01 2012        (r242028)
> +++ head/sys/kern/subr_param.c  Thu Oct 25 01:46:20 2012        (r242029)
> @@ -278,8 +278,16 @@ init_param2(long physpages)
>                 maxusers = physpages / (2 * 1024 * 1024 / PAGE_SIZE);
>                 if (maxusers < 32)
>                         maxusers = 32;
> -               if (maxusers > 384)
> -                       maxusers = 384;
> +               /*
> +                * Clips maxusers to 384 on machines with <= 4GB RAM or 32bit.
> +                * Scales it down 6x for large memory machines.
> +                */
> +               if (maxusers > 384) {
> +                       if (sizeof(void *) <= 4)
> +                           maxusers = 384;
> +                       else
> +                           maxusers = 384 + ((maxusers - 384) / 6);

    Why `/ 6` (other than the fact that it makes the value presumably
a multiple of 64)? Also, shouldn't some kind of clamping be taking
place to ensure that this the end result of the calculation is a
multiple of a power of two, e.g. 16, 32, 64, etc?
    And as usual, got ministat :)?
Thanks!
-Garrett