Running offload application on Xeon-Phi
- Execute the following command on Xeon in order to run offload application:
It is possible to generate diagnostic output for offload applications that utilize Intel Xeon Phi coprocessors.
The Linux environment variable OFFLOAD_REPORT controls the verbosity of the diagnostic output:
a) When this variable is not set or has the value 0, no diagnostic output is produced.
b) Setting OFFLOAD_REPORT=1 produces output including the offload locations and times.
c) Setting OFFLOAD_REPORT=2, in addition, produces information regarding data traffic.
- How to configure environment variables to be used in offload application
Environment variables defined on the host are automatically
forwarded to the coprocessor when an offload application is launched.
By default, variable names are not changed on the coprocessor.
In order to avoid environment variable name collisions on the host and
the coprocessor, the user can utilize the environment variable
MIC_ENV_PREFIX. When this variable is set, only environment variables
with names beginning with the specified prefix are be forwarded, and
the prefix is stripped on the coprocessor.
Note that the variable MIC_LD_LIBRARY_PATH is an exception. It is never
passed to the coprocessor with its suffix stripped, so it is not
possible to change the value of LD_LIBRARY_PATH on the coprocessor
using environment forwarding.
- OMP_NUM_THREADS Environment Variable
When an offload application is
launched, the computation can be split on the processor and
coprocessor. In this case the environment variable that defines the
number of threads, OMP_NUM_THREADS, is the same for both, but if you
want a different number of threads running in the coprocessor, you can
set the environment variable as follow:
• export MIC_ENV_PREFIX=MIC
• export MIC_OMP_NUM_THREADS=240
• export OMP_NUM_THREADS=32
In this example, we will have 240 threads running in the coprocessor and 32 threads running in the processor.
- KMP_AFFINITY Environment Variable
Thread affinity in OpenMP applications can be controlled at the application level by setting the environment variable KMP_AFFINITY.
The format of the variable is
Note that in order to use different affinity masks on the host and on
coprocessors with offload applications, the environment variable
MIC_ENV_PREFIX may be set. For example, the setup below
results in affinity type compact on the host and balanced
on the coprocessor.
In order to lear more about thread affinity on Intel Xeon-Phi, use this link:
- user@host% export MIC_ENV_PREFIX=MIC
- user@host% export KMP_AFFINITY=compact,granularity=fine
- user@host% export MIC_KMP_AFFINITY=balanced,granularity=fine