perftest: support set flow_label through env variable FLOW_LABEL

[changchengx]

• What Add user parameter --flow_label=<value> to be set by user to affect the udp sport calculation.
• Why When some customer report the problem while testing under 1) case one: RoCE LAG 2) case two: not back-to-back connected, the udp sport is randomly selected and make the test result unstable. With adding --flow_label=<value> to set the grh flow_label value, it can be used to afftect the udp sport to 1) use same tx port for traffic 2) walk through same traffic path between different round of test when the cards are connected with using switches.

[changchengx]

Follow below steps to build perftest with this PR

git clone https://github.com/linux-rdma/perftest.git
cd perftest
wget https://github.com/linux-rdma/perftest/pull/224.diff
git apply 224.diff
./autogen.sh
mkdir install
./configure --prefix=$PWD/install
make
make install

Follow below steps to run ib_write_lat with this PR

1. Server

   taskset -c 2 ./install/bin/ib_write_lat -F -s 2 --tclass=106 --ib-dev=mlx5_bond_0 -x 3 -D 60

   Note: add FLOW_LABEL=xxx before taskset to run the command if it needs to specify flow_label value.

2. Client

   taskset -c 2 ./install/bin/ib_write_lat -F -s 2 --tclass=106 --ib-dev=mlx5_bond_0 -x 3 -D 60 ${server_ip}

   Note: add FLOW_LABEL=xxx before taskset to run the command if it needs to specify flow_label value.

[changchengx]

@HassanKhadour Please help review this PR when you're avaiable.

[HassanKhadour]

Hi @changchengx , thanks for your contribution! Is there any reason why not to add the flow_label as perftest param? also please update the man page and the commit message to include the data in https://github.com/linux-rdma/perftest/pull/224#issue-1853239069

[changchengx]

@HassanKhadour Do you prefer to add flow_label as perftest param instead of using environment variable to set flow_label?

[HassanKhadour]

@changchengx yes it would be the preferred option

[changchengx]

@changchengx yes it would be the preferred option

@HassanKhadour Feedback to you later.

[changchengx]

@changchengx yes it would be the preferred option

@HassanKhadour Feedback to you later.

@HassanKhadour Done

[HassanKhadour]

@changchengx yes it would be the preferred option

@HassanKhadour Feedback to you later.

@HassanKhadour Done

Thanks!, just a small fix, and please add data to the commit message as you did in https://github.com/linux-rdma/perftest/pull/224#issue-1853239069

[changchengx]

@HassanKhadour

1. used return FAILURE
2. Added commit msg to explain this PR.

[HassanKhadour]

@changchengx Thanks for your contribution! merged