[mvapich-discuss] Assumptions about page size in OSU benchmarks

[Dhabaleswar Panda]

Hi Mark, 

Thanks for reporting this. 

We will update the OSU benchmarks to handle large page size.

Thanks, 

DK

> I was running the OSU benchmarks on a SiCortex system recently, and hit
> a bus error with osu_bw.c. The MPI folks at SiCortex discovered the
> cause of the problem, and it was due to the value of MAX_ALIGNMENT being
> set too low. These systems have a 64K page size and the effect of the
> alignment adjustment code is to cause a buffer over-run:
> 
> #define MAX_ALIGNMENT 16384
> #define MAX_MSG_SIZE (1<<22)
> #define MYBUFSIZE (MAX_MSG_SIZE + MAX_ALIGNMENT)
> 
> ...
> 
> char s_buf1[MYBUFSIZE];
> char r_buf1[MYBUFSIZE];
> 
> ...
> 
>     align_size = getpagesize();
>     s_buf =
>         (char *) (((unsigned long) s_buf1 + (align_size - 1)) /
>                   align_size * align_size);
>     r_buf =
>         (char *) (((unsigned long) r_buf1 + (align_size - 1)) /
>                   align_size * align_size);
> 
> I suggest increasing MAX_ALIGNMENT to at least 65536 bytes, and add
> a run-time check that gives a suitable diagnostic if getpagesize() 
> is larger than MAX_ALIGNMENT. Alternatively you could dynamically
> allocate the arrays, perhaps using posix_memalign, to avoid
> the problem. This affects osu_bw.c,  osu_bibw.c and osu_mbw_mr.c 
> though I did not check all of the benchmarks for this.
> 
> Regards,
> 
> Mark Debbage.
> 
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