we use YCSB to stress mongodb 3.6 vs 3.4, storage wiredTiger.

We found that 3.6 slower than 3.4 about 50%. We test 5 times, results as below, the number is qps( only insert thest)

3.6.4 | 3.4.14
------ | ------
17757 | 18622
17695 | 18841
15910 | 18265
16378 | 18504
16142 | 18480

YCSB's workload:

<noformat>
recordcount=100000000
operationcount=100000000
workload=com.yahoo.ycsb.workloads.CoreWorkload
threadcount = 50

readallfields=true

readproportion=0
updateproportion=0
scanproportion=0
insertproportion=1
readmodifywriteproportion=0

requestdistribution=zipfian
insertorder = hashed
readallfields=true
fieldlength = 200
fieldcount = 10
mongodb.writeConcern = acknowledged
mongodb.database = ycsb
mongodb.url = mongodb://192.168.1.2:27017/admin
table = ycsbtest
<noformat>

mongod's configuration as below:

<noformat>
dbpath=/home/mongo/data
syslog=true
logappend=true
bind_ip = 127.0.0.1,192.168.1.2
port = 27017

cpu = true
noauth = true

maxConns = 65535

smallfiles = true
noprealloc = true
oplogSize = 20000
wiredTigerDirectoryForIndexes = true
directoryperdb = true
wiredTigerCacheSizeGB = 16
storageEngine = wiredTiger
<noformat>

we also test:
1. replication set, but 3.6.4 is much slower too.
2. networkMessageCompressors = disabled under 3.6, no positive feedback.

1. The hardware/network/OS exactly the same(the same machine).
2. nofile/nproc both changed to 65536
3. no firewall
4. OS is Debian 9 amd64
5. SSD