svn commit: r208165 - in head/sys: kern mips/conf mips/include mips/mips mips/rmi mips/rmi/dev/xlr

[Attilio Rao]

2010/8/9 Jayachandran C. <c.jayachandran at gmail.com>:
> On Mon, Aug 9, 2010 at 5:31 AM, Attilio Rao <attilio at freebsd.org> wrote:
>> 2010/5/16 Randall Stewart <rrs at freebsd.org>:
>>> Author: rrs
>>> Date: Sun May 16 19:43:48 2010
>>> New Revision: 208165
>>> URL: http://svn.freebsd.org/changeset/base/208165
>>>
>>> Log:
>>>  This pushes all of JC's patches that I have in place. I
>>>  am now able to run 32 cores ok.. but I still will hang
>>>  on buildworld with a NFS problem. I suspect I am missing
>>>  a patch for the netlogic rge driver.
>>>
>>>  JC check and see if I am missing anything except your
>>>  core-mask changes
>>
>>
>>> Modified: head/sys/kern/subr_smp.c
>>> ==============================================================================
>>> --- head/sys/kern/subr_smp.c    Sun May 16 19:25:56 2010        (r208164)
>>> +++ head/sys/kern/subr_smp.c    Sun May 16 19:43:48 2010        (r208165)
>>> @@ -503,7 +503,10 @@ smp_topo_none(void)
>>>        top = &group[0];
>>>        top->cg_parent = NULL;
>>>        top->cg_child = NULL;
>>> -       top->cg_mask = (1 << mp_ncpus) - 1;
>>> +       if (mp_ncpus == sizeof(top->cg_mask) * 8)
>>> +               top->cg_mask = -1;
>>> +       else
>>> +               top->cg_mask = (1 << mp_ncpus) - 1;
>>>        top->cg_count = mp_ncpus;
>>>        top->cg_children = 0;
>>>        top->cg_level = CG_SHARE_NONE;
>>>
>>
>> ... and this is why I particulary hate big commits with complete lack
>> of technical details.
>>
>> This particulary chunk was supposed to fix a nasty and completely MI
>> bug that some users have already met (kern/148698). The complete lack
>> of details didn't help in identify the issue neither that it was a
>> valuable fix.
>>
>> The fix is, however, improper (there is no clear relationship between
>> the multiplication and why that happens) thus I would rather use what
>> Joe has reported in the PR.
>
>
> I was not aware of the PR when I sent this changes to rrs@, and this
> went as a part of MIPS SMP support for XLR which has 32 CPUs
>
> But I'm not sure that the current change is correct, cg_mask is of
> type cpumask_t and I don't think it is guaranteed to be 32 bit (as it
> is a machine dependent type).

Actually the 32 bits limit is well aware and acknowledged in cpumask_t.
While it is true that it should be an 'opaque' type, in reality it is
not. The maximum limit of 32 CPUs is a reality due to cpumask_t on all
our architectures.
That is why we are going to use cpuset_t for dealing with CPUs numbers
(which is really opaque, at same extent, and is not bound to any
size).

Attilio


-- 
Peace can only be achieved by understanding - A. Einstein