Galera is 3x slower than standalone with durable settings

When comparing a single-node Galera with a standalone MariaDB, I have noticed a suspiciously big performance difference with durable/non-durable settings:

1. Galera is 3x slower than standalone, both with durable settings
2. Durable Galera is 3x slower than non-durable Galera

Config:

[mysqld]

# durable

sync_binlog=1

innodb_flush_log_at_trx_commit=1

# non-durable

# sync_binlog=0

# innodb_flush_log_at_trx_commit=2

max_connections=2000

query_cache_type=0

query_cache_size=0

log_bin=1

binlog_format=ROW

log_slave_updates=1

innodb_flush_method=O_DIRECT

innodb_buffer_pool_size=4000M

innodb_buffer_pool_instances=4

innodb_log_buffer_size=64M

[galera]

wsrep_on=ON

wsrep_provider=/usr/lib64/galera/libgalera_smm.so

innodb-autoinc-lock-mode=2

wsrep_cluster_name=galera

wsrep_node_address=node1

wsrep_node_name=node1

wsrep_cluster_address=gcomm://

wsrep_sst_method=rsync

wsrep_slave_threads=8

Benchmark: Sysbench 0.5

sysbench \

--test=/usr/share/doc/sysbench/tests/db/oltp.lua \

--mysql-host=localhost \

--mysql-user=root \

--oltp-table-size=1000000 \

--num-threads=128 \

--max-requests=0 \

--max-time=60 \

run

Results:

Galera, durable
read/write requests: 4994.74 per sec.

Standalone, durable
read/write requests: 16858.99 per sec.

Galera, non-durable
read/write requests: 15938.04 per sec.

Standalone, non-durable
read/write requests: 17055.88 per sec.

Server details:

2 Cores

8 GB RAM

SSD

I have repeated the tests multiple times, even re-bootstrapped the data directory and Galera.

What is also interesting, the CPU idle stays above 50% with the durable Galera, while it stays under 1% in other testing scenarios.

Update:
Changing wsrep_slave_threads to 4, innodb_buffer_pool_instances to 2 and including innodb-autoinc-lock-mode=2 in mysqld didn't change anything.

Another interesting thing: iowait is over 20% with the durable Galera, while it is under 1% in other scenarios.