Samba Perfomance issues are seen when "async smb echo handler" is enabled

Issue

When the following option is enabled in samba we see a dramatic loss in throughput performance.

async smb echo handler = yes

Output which shows throughput performances in different scenario's.

Option disabled (async smb echo handler = no)

# dd if=/dev/zero of=test_pup_1g bs=1G count=1
1+0 records in
1+0 records out
1073741824 bytes (1.1 GB) copied, 3.07757 s, 349 MB/s

Option enabled (async smb echo handler = yes)

# dd if=/dev/zero of=test_pup_1g bs=1G count=1
1+0 records in
1+0 records out
1073741824 bytes (1.1 GB) copied, 188.025 s, 5.7 MB/s