[mpich-discuss] MPI_WIN_LOCK and MPI_MODE_NOCHECK assert

[Jim Dinan]

Hi Jaric,

I pushed out the MODE_NOCHECK changes as a part of 9e68dcf86.  Feel free 
to try them out.

Best,
  ~Jim.

On 2/21/13 9:20 AM, Jim Dinan wrote:
> Hi Jaric,
>
> In current and previous releases of MPICH, MPI_MODE_NOCHECK was only
> used to optimize active target communication.  As part of the MPI-3
> work, we've also added a MPI_MODE_NOCHECK optimization to passive target
> communication.  This feature should hopefully make it out to our git
> repo this week and be included in the in the next release.
>
> MPI_MODE_NOCHECK essentially asserts that the epoch can begin
> immediately at the target.  If you are using exclusive locks, this means
> that the lock is uncontended.  If you are using shared locks, this means
> that the lock is uncontended, or that all other processes are also using
> shared lock.
>
> In terms of the implementation for passive target, MODE_NOCHECK allows
> us to piggyback the lock request on the first RMA operation, since the
> user has asserted that the lock request will succeed immediately.
>
> Best,
>   ~Jim.
>
> On 2/20/13 9:11 PM, Jaroslaw Zola wrote:
>> I have a question regarding implementation of the MPI_MODE_NOCHECK
>> assertion
>> for MPI_WIN_LOCK. Is current mpich implementation taking advantage of
>> this
>> hint? Also, according to the standard:
>>
>> MPI_MODE_NOCHECK - no other process holds, or will attempt to acquire,
>> a conflicting lock, while the caller holds the window lock. This is
>> useful when
>> mutual exclusion is achieved by other means, but the coherence
>> operations that
>> may be attached to the lock and unlock calls are still required.
>>
>> Are two concurrent locks from two different MPI processes followed by
>> MPI_GET
>> (i.e. given window is not modified but read only) considered conflicting?
>>
>> Thanks!
>>
>> - Jaric
>>
>>
>>
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