I’m trying to pipe extremely high speed data from one application to another using 64-bit CentOS6. I have done the following benchmarks using dd to discover that the pipes are holding me back and not the algorithm in my program. My goal is to achieve somewhere around 1.5 GB/s.
First, without pipes:
dd if=/dev/zero of=/dev/null bs=8M count=1000 1000+0 records in 1000+0 records out 8388608000 bytes (8.4 GB) copied, 0.41925 s, 20.0 GB/s
Next, a pipe between two dd processes:
dd if=/dev/zero bs=8M count=1000 | dd of=/dev/null bs=8M 1000+0 records in 1000+0 records out 8388608000 bytes (8.4 GB) copied, 9.39205 s, 893 MB/s
Are there any tweaks I can make to the kernel or anything else that will improve performance of running data through a pipe? I have tried named pipes as well, and gotten similar results.
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Answer
Have you tried with smaller blocks?
When I try on my own workstation I note successive improvement when lowering the block size. It is only in the realm of 10% in my test, but still an improvement. You are looking for 100%.
As it turns out testing further, really small block sizes seem to do the trick:
I tried
dd if=/dev/zero bs=32k count=256000 | dd of=/dev/null bs=32k 256000+0 records in 256000+0 records out 256000+0 records in 256000+0 records out 8388608000 bytes (8.4 GB) copied8388608000 bytes (8.4 GB) copied, 1.67965 s, 5.0 GB/s , 1.68052 s, 5.0 GB/s
And with your original
dd if=/dev/zero bs=8M count=1000 | dd of=/dev/null bs=8M 1000+0 records in 1000+0 records out 1000+0 records in 1000+0 records out 8388608000 bytes (8.4 GB) copied8388608000 bytes (8.4 GB) copied, 6.25782 s, 1.3 GB/s , 6.25203 s, 1.3 GB/s
5.0/1.3 = 3.8 so that is a sizable factor.