Speed up LSF

I am using LSF to send logs that are written in a file. The amount of data written is very large (around 5 millions) and I'd like to send it quickly. The problem I am facing is that LSF sends information quite slowly and I'd like to speed it up.
I tried to change come configuration options such as spool-size and harvester-buff-size, but I improved nothing.
Does anyone know how to do it?

Thanks in advance!

How do you know that it's LSF that can't keep up and that the receiving end is able to process the data fast enough? Logstash basically has no internal buffer so its output rate determines its input rate.

To be honest, I don't know if the "problem" is in LSF or in logstash. From reading LSF output, I assumed it was in LSF, but now I don't know.
I'll keep looking into it and if I find out something, I'll post here.