[mpich2-dev] [opa-core] Problem with MPICH2 1.1 during MPI_Init() on PPC Linux 32bit

[Dave Goodell]

[adding Sameer]

On Jun 9, 2009, at 3:23 PM, Darius Buntinas wrote:

> I see that there is a comment in opa_gcc_ppc.h that "these need to be
> aligned on an 8-byte boundary to work on a BG/P."  Do you know if this
> is true?
>
> Dave, this looks like your comment.  Can you comment?

This was a restriction that Sameer told me was needed for lwarx/stcwx  
to preserve atomicity on BG/P when we visited Watson last summer.  I  
don't know for sure whether or not it is needed, I just took Sameer's  
statement at face value.

> Should this be changed to "OPA_ATTRIBUTE((aligned (SIZEOF_VOID_P)))"  
> to
> handle different pointer sizes (similarly for SIZEOF_INT for ints)?

I think the bigger question is whether or not the assertion is  
sensible.  I don't know why the cell rel pointer structure needs to be  
exactly the same size as a pointer as long as it contains a pointer  
value...

> -d
>
> On 06/09/2009 03:04 PM, Joe Ratterman wrote:
>> This is the error I'm seeing:
>>
>>    Assertion failed in file mpid_nem_init.c at line 89:
>>    sizeof(MPID_nem_cell_rel_ptr_t) == 4
>>
>>
>>
>> This appears to be the important code from the pre-processed version
>> of mpid_nem_init.c
>>
>>
>>    # 11
>>    "/bglhome/usr1/jratt/src-sles10/mpich2/mpich2-1.1/src/openpa/src/ 
>> primitives/opa_gcc_ppc.h"
>>    typedef struct { volatile int v __attribute__ ((aligned (8))); }
>>    OPA_int_t;
>>    typedef struct { void * volatile v __attribute__ ((aligned  
>> (8))); }
>>    OPA_ptr_t;
>>
>>    # 188 "../include/mpid_nem_datatypes.h"
>>    typedef struct MPID_nem_cell_rel_ptr
>>    {
>>        OPA_ptr_t p;
>>    }
>>    MPID_nem_cell_rel_ptr_t;
>>
>>    # 135 mpid/ch3/include/mpidi_ch3_conf.h
>>
>>    #define SIZEOF_VOID_P 4
>>
>>    # 85 mpid_nem_init.c
>>        /* The MPID_nem_cell_rel_ptr_t defined in mpid_nem_datatypes.h
>>         * should only contain a pointer. Also, we don't support  
>> compilers
>>         * which add random padding to the start of the structure. The
>>         * below assert should blow up if any of these happens. */
>>        MPIU_Assert(sizeof(MPID_nem_cell_rel_ptr_t) == SIZEOF_VOID_P);
>>
>>
>>
>> Given the above code, the size of that type appears to be 8 in both  
>> GCC
>> and XLC.  I see that the alignment is hard-coded to 8 in
>> src/openpa/src/primitives/opa_gcc_ppc.h.  Changing that first line  
>> to an
>> alignment of 4, the type size shrinks to 4 (correspondingly,  
>> increasing
>> it to 16 increases the type size as well).
>>
>> Changing the file to 4 and recompiling things allows a few simple  
>> tests
>> to work fine--I haven't tried too much more.
>>
>>
>>
>> Thanks,
>> Joe Ratterman
>> jratt at us.ibm.com <mailto:jratt at us.ibm.com>
>>
>>
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