User guide

6–SHMEM Description and Configuration
Environment Variables
IB0054606-02 A 6-13
 SHMEM's long message protocol is disabled. This is because the long
message protocol implementation does not support passive progress. The
effect of disabling this is to reduce long message bandwidth to that which
can be achieved with the short message protocol. There is no effect on the
bandwidth for message sizes below the long message break-point, which is
set to 16KB by default.
Active versus Passive Progress
It is expected that most applications will be run with QLogic SHMEM's active
progress mode since this gives full performance. The passive progress mode will
typically be used in the following circumstances:
 For applications that use a polling idiom that is incompatible with the active
progress mode, and where the application programmer is unable or
unwilling to recode to use the appropriate SHMEM wait primitive.
 For compliance to a SHMEM standard that has a passive progress
requirement.
Environment Variables
Table 6-1 list the environment variables that are currently provided by the SHMEM
run time library.
NOTE
The set of supported environment variables and their defaults may
vary.from release to release.
Table 6-1. SHMEM Run Time Library Environment Variables
Environment Variable Default Description
$SHMEM_SHMALLOC_INIT_SIZE 16MB Initial size of the global shared memory
segment.
$SHMEM_SHMALLOC_MAX_SIZE 4GB Maximum size of the global shared
memory segment.