performance difference between dd and elbencho

[jbd]

Hello,

I'm trying to understand the performance difference between elbencho and dd, both using directio on a local nvme drive. dd is showing 2 GBytes/s and elbench around 900 MBytes/s.

$ elbencho --version
elbencho
 * Version: 3.0-26
 * Net protocol version: 3.0.23
 * Build date: Feb 19 2025 17:39:42
 * Included optional build features: backtrace corebind libaio libnuma ncurses syncfs syscallh 
 * Excluded optional build features: althttpsvc cuda cufile/gds hdfs mimalloc s3 s3crt 
 * System steady clock precision: 1e-09 sec

The elbencho run:

$ elbencho -w -b 4M -t 1 --blockvarpct 0 --direct -s 10g /local/scratch/tmp/file_elbencho 
OPERATION   RESULT TYPE         FIRST DONE   LAST DONE
=========== ================    ==========   =========
WRITE       Elapsed time     :     11.559s     11.559s
            IOPS             :         221         221
            Throughput MiB/s :         885         885
            Total MiB        :       10240       10240
---

And the dd run:

$ dd if=/dev/zero of=/local/scratch/tmp/file_dd oflag=direct bs=4M count=2560 status=progress
9739173888 bytes (9.7 GB, 9.1 GiB) copied, 5 s, 1.9 GB/s
2560+0 records in
2560+0 records out
10737418240 bytes (11 GB, 10 GiB) copied, 5.5149 s, 1.9 GB/s

I feel that I'm missing something obvious here. Any suggestions ?

Thank you !