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Subject: Re: [OMPI devel] Duplicated modex issue.
From: Ralph Castain (rhc_at_[hidden])
Date: 2012-12-21 10:11:13


Don't know how many times I can repeat it, but I'll try again: you are not allowed to reuse a collective id. If it happens to work, it's by accident.

If you want to implement multiple modex/barrier operations, they each need to have their own unique collective id.

On Dec 20, 2012, at 9:28 PM, Victor Kocheganov <victor.kocheganov_at_[hidden]> wrote:

> Actually, if I reuse id's in equivalent calls like this:
> ...
> 'modex' block;
> 'modex' block;
> 'modex' block;
> ...
> or
> ...
> 'barrier' block;
> 'barrier' block;
> 'barrier' block;
> ...
> there is no hanging. The hang only occurs if this "reusing" follows after using of another collective id, In the way I wrote in the first letter:
> ...
> 'modex' block;
> 'barrier' block;
> 'modex' block; <- hangs
> ...
> or in this way
> ...
> 'barrier' block;
> 'modex' block;
> 'barrier' block; <- hangs
> ...
>
> If I use different collective id while calling modex (1, 2 , ... , but not 0==orte_process_info.peer_modex), that also won't work, unfortunately..
>
>
>
> On Thu, Dec 20, 2012 at 10:39 PM, Ralph Castain <rhc_at_[hidden]> wrote:
> Yeah, that won't work. The id's cannot be reused, so you'd have to assign a different one in each case.
>
> On Dec 20, 2012, at 9:12 AM, Victor Kocheganov <victor.kocheganov_at_[hidden]> wrote:
>
>> In every 'modex' block I use coll->id = orte_process_info.peer_modex; id and in every 'barrier' block I use coll->id = orte_process_info.peer_init_barrier; id.
>>
>> P.s. In general (as I wrote in first letter), I use 'modex' term for following code:
>> coll = OBJ_NEW(orte_grpcomm_collective_t);
>> coll->id = orte_process_info.peer_modex;
>> if (ORTE_SUCCESS != (ret = orte_grpcomm.modex(coll))) {
>> error = "orte_grpcomm_modex failed";
>> goto error;
>> }
>> /* wait for modex to complete - this may be moved anywhere in mpi_init
>> * so long as it occurs prior to calling a function that needs
>> * the modex info!
>> */
>> while (coll->active) {
>> opal_progress(); /* block in progress pending events */
>> }
>> OBJ_RELEASE(coll);
>>
>> and 'barrier' for this:
>>
>> coll = OBJ_NEW(orte_grpcomm_collective_t);
>> coll->id = orte_process_info.peer_init_barrier;
>> if (ORTE_SUCCESS != (ret = orte_grpcomm.barrier(coll))) {
>> error = "orte_grpcomm_barrier failed";
>> goto error;
>> }
>> /* wait for barrier to complete */
>> while (coll->active) {
>> opal_progress(); /* block in progress pending events */
>> }
>> OBJ_RELEASE(coll);
>>
>> On Thu, Dec 20, 2012 at 8:57 PM, Ralph Castain <rhc_at_[hidden]> wrote:
>>
>> On Dec 20, 2012, at 8:29 AM, Victor Kocheganov <victor.kocheganov_at_[hidden]> wrote:
>>
>>> Thanks for fast answer, Ralph.
>>>
>>> In my example I use different collective objects. I mean in every mentioned block I call coll = OBJ_NEW(orte_grpcomm_collective_t);
>>> and OBJ_RELEASE(coll); , so all the grpcomm operations use unique collective object.
>>
>> How are the procs getting the collective id for those new calls? They all have to match
>>
>>>
>>>
>>> On Thu, Dec 20, 2012 at 7:48 PM, Ralph Castain <rhc_at_[hidden]> wrote:
>>> Absolutely it will hang as the collective object passed into any grpcomm operation (modex or barrier) is only allowed to be used once - any attempt to reuse it will fail.
>>>
>>>
>>> On Dec 20, 2012, at 6:57 AM, Victor Kocheganov <victor.kocheganov_at_[hidden]> wrote:
>>>
>>>> Hi.
>>>>
>>>> I have an issue with understanding ompi_mpi_init() logic. Could you please tell me if you have any guesses about following behavior.
>>>>
>>>> I wonder if I understand ringh, there is a block in ompi_mpi_init() function for exchanging procs information between processes (denote this block 'modex'):
>>>> coll = OBJ_NEW(orte_grpcomm_collective_t);
>>>> coll->id = orte_process_info.peer_modex;
>>>> if (ORTE_SUCCESS != (ret = orte_grpcomm.modex(coll))) {
>>>> error = "orte_grpcomm_modex failed";
>>>> goto error;
>>>> }
>>>> /* wait for modex to complete - this may be moved anywhere in mpi_init
>>>> * so long as it occurs prior to calling a function that needs
>>>> * the modex info!
>>>> */
>>>> while (coll->active) {
>>>> opal_progress(); /* block in progress pending events */
>>>> }
>>>> OBJ_RELEASE(coll);
>>>> and several instructions after this there is a block for processes synchronization (denote this block 'barrier'):
>>>> coll = OBJ_NEW(orte_grpcomm_collective_t);
>>>> coll->id = orte_process_info.peer_init_barrier;
>>>> if (ORTE_SUCCESS != (ret = orte_grpcomm.barrier(coll))) {
>>>> error = "orte_grpcomm_barrier failed";
>>>> goto error;
>>>> }
>>>> /* wait for barrier to complete */
>>>> while (coll->active) {
>>>> opal_progress(); /* block in progress pending events */
>>>> }
>>>> OBJ_RELEASE(coll);
>>>> So, initially ompi_mpi_init() has following structure:
>>>> ...
>>>> 'modex' block;
>>>> ...
>>>> 'barrier' block;
>>>> ...
>>>> I made several experiments with this code and the following one is of interest: if I add sequence of two additional blocks, 'barrier' and 'modex', right after 'modex' block, then ompi_mpi_init() hangs in opal_progress() of the last 'modex' block.
>>>> ...
>>>> 'modex' block;
>>>> 'barrier' block;
>>>> 'modex' block; <- hangs
>>>> ...
>>>> 'barrier' block;
>>>> ...
>>>> Thanks,
>>>> Victor Kocheganov.
>>>> _______________________________________________
>>>> devel mailing list
>>>> devel_at_[hidden]
>>>> http://www.open-mpi.org/mailman/listinfo.cgi/devel
>>>
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