I am testing on x86_64 platform. I have tried to built both the mpich and the mcs lock code with -O0 to avoid agressive optimization. After your suggestion I have also tried to make volatile int *pblocked pointing to lmem[blocked] in the MCSLockAcquire function and volatile int *pnextrank pointing to lmem[nextRank] in MCSLockRelease, but it does not appear to make a difference. On suggestion from Richard Warren I have also tried building the code using openmpi-2.0.2 without any luck (however it appears to acquire the lock a couple of extra times before failing) which I find troubling. I think I will give up using local load/stores and will see if I can figure out if rewrite using MPI calls like MPI_Fetch_and_op as you suggest. Thanks for your help. On Mon, Mar 6, 2017 at 7:20 PM, Jeff Hammond <[email protected]> wrote:

What processor architecture are you testing?

Maybe set lmem to volatile or read it with MPI_Fetch_and_op rather than a load. MPI_Win_sync cannot prevent the compiler from caching *lmem in a register.

Jeff

On Sat, Mar 4, 2017 at 12:30 AM, Ask Jakobsen <[email protected]> wrote:

...

Hi,

I have downloaded the source code for the MCS lock from the excellent book "Using Advanced MPI" from http://www.mcs.anl.gov/researc h/projects/mpi/usingmpi/examples-advmpi/rma2/mcs-lock.c

I have made a very simple piece of test code for testing the MCS lock but it works at random and often never escapes the busy loops in the acquire and release functions (see attached source code). The code appears semantically correct to my eyes.

#include <stdio.h> #include <mpi.h> #include "mcs-lock.h"

int main(int argc, char *argv[]) { MPI_Win win; MPI_Init( &argc, &argv );

MCSLockInit(MPI_COMM_WORLD, &win);

int rank, size; MPI_Comm_rank(MPI_COMM_WORLD, &rank); MPI_Comm_size(MPI_COMM_WORLD, &size);

printf("rank: %d, size: %d\n", rank, size);

MCSLockAcquire(win); printf("rank %d aquired lock\n", rank); fflush(stdout); MCSLockRelease(win);

MPI_Win_free(&win); MPI_Finalize(); return 0; }

I have tested on several hardware platforms and mpich-3.2 and mpich-3.3a2 but with no luck.

It appears that the MPI_Win_Sync are not "refreshing" the local data or I have a bug I can't spot.

A simple unfair lock like http://www.mcs.anl.gov/researc h/projects/mpi/usingmpi/examples-advmpi/rma2/ga_mutex1.c works perfectly.

Best regards, Ask Jakobsen

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-- Jeff Hammond [email protected] http://jeffhammond.github.io/

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