How to set multiple logstash for only one logfile?

My log-server specification is not good(RAM 8g, cpu 2.4GHz).
So I disappointed for slowly collecting log.
I checked my logstash performance(about 400/eps) through elasticsearch count.
I already tried using two logstash, But just collected double-size log.
I want multiple logstash for one log-file.
If that is possible, How can I set multiple logstash?

I don't set logstash, elasticsearch configuration except logstash.conf.
if I set logstash, elasticsearch configuration, how speed increase ?
Let me know, configuration detailed.

logstash.conf

input
{
file
{
path => ["C:/logs/filelog_%{+YYYY-MM-dd}.csv"]
type => "sdkNormalLog"
}
}

output
{
elasticsearch
{
hosts => "127.0.0.1:9200"
}
}

test result

2016.04.11 13:45 start 2600400
2016.04.11 14:06 end 3200400

600000
test result : 476/eps, 28571/epm,

What version are you running? What JVM?
Did you try increasing workers or threads?

Does that even work? I haven't seen it before.

logstash 2.3.0 , elasticsearch 2.3.0

java 1.8.0 77

I don't know how to increase workers or threads?

is it output option in logstash configuration ?

I saw that logstash start >> Settings : Default pipeline workers: 4

Does that even work? I haven't seen it before.
~>>>>> yes, good to work. that path mean today.

You should upgrade LS to 2.3.1, there were a few problems with the 2.3.0 release.