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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.

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