QA.md

Question and Answer

Table of Contents

• Performance has a large range of error

Q1: Enable the transparent hugepage (THP)

The results of SPARQL queries on my machine has a large difference to the results in docs/performance and/or research papers. How to tune the performance of SPARQL queries on Wukong?

wukong> sparql -f sparql_query/lubm/basic/lubm_q1 -m 16 -n 10
...
INFO:     (average) latency: 2113299 usec
INFO:     (last) result size: 2528
wukong> sparql -f sparql_query/lubm/basic/lubm_q1 -m 16 -n 10
...
INFO:     (average) latency: 5234887 usec
INFO:     (last) result size: 2528
wukong> sparql -f sparql_query/lubm/basic/lubm_q1 -m 16 -n 10
...
INFO:     (average) latency: 1793383 usec
INFO:     (last) result size: 2528

Answer

Please check if transparent hugepages (THP) is enabled. If it has been disabled (i.e., [never]), then you should enable THP before running Wukong.

$ cat /sys/kernel/mm/transparent_hugepage/enabled
always madvise [never]

Transparent Hugepage Support can be enabled in system wide or only enabled inside MADV_HUGEPAGE regions (to avoid the risk of consuming more memory resources) or disabled entirely. This can be achieved with one of:

$ echo always > /sys/kernel/mm/transparent_hugepage/enabled
$ echo madvise > /sys/kernel/mm/transparent_hugepage/enabled
$ echo never > /sys/kernel/mm/transparent_hugepage/enabled

Perhaps the command fails as following.

$ echo always > /sys/kernel/mm/transparent_hugepage/enabled
-bash: enabled: Permission denied

Then you can try one of these commands.

$ sudo bash -c "echo always > /sys/kernel/mm/transparent_hugepage/enabled"
$ sudo bash -c "echo madvise > /sys/kernel/mm/transparent_hugepage/enabled"
$ sudo bash -c "echo never > /sys/kernel/mm/transparent_hugepage/enabled"