You can enable libhugetlbfs on more complex workloads such as MySQL and test the results after enabling it.
Before proceeding, you should be familiar with building and running MySQL. Refer to Benchmarking MySQL with Sysbench for more information. The steps below explain how to modify the build and run of MySQL server to enable libhugtlbfs (full instructions are not provided).
In order to build MySQL with libhugetlbfs support, you add the following options to both -DCMAKE_C_FLAGS and -DCMAKE_CXX_FLAGS:
-B /usr/share/libhugetlbfs -Wl,--hugetlbfs-align -no-pie -Wl --no-as-needed
If you look at the cmake command in the
Build and install MySQL server
section you will see the cmake command to modify.
The new cmake command is:
cmake -DCMAKE_C_FLAGS="-g -mcpu=native -B /usr/share/libhugetlbfs -Wl,--hugetlbfs-align -no-pie -Wl,--no-as-needed" -DCMAKE_CXX_FLAGS="-g -mcpu=native -B /usr/share/libhugetlbfs -Wl,--hugetlbfs-align -no-pie -Wl,--no-as-needed" -DCMAKE_INSTALL_PREFIX=/home/mysql/mysql_install/1-install_8.0.33_huge -DWITH_BOOST=/home/mysql/boost_1_77_0/ ..
The 2 make commands are the same:
make -j $(nproc)
make -j $(nproc) install
After the build completes, check if the program has linked with libhugetlbfs.so, for example:
ldd mysqld | grep huge
The output should show libhugetlbfs is being used.
libhugetlbfs.so.0 => /lib/aarch64-linux-gnu/libhugetlbfs.so.0 (0x0000ffffac690000)
After rebuilding MySQL with libhugetlbfs, add HUGETLB_ELFMAP=RW at the beginning of the commands that start MySQL.
This is an addition to the information in the
Start the MySQL server
section. Add the variable before each invocation of mysql.
For example:
HUGETLB_ELFMAP=RW /home/mysql/mysql_install/1-install_8.0.33_huge/bin/mysqld ...
Do not export HUGETLB_ELFMAP=RW as an environment variable, it has to be specified right before the mysqld executable.
Testing MySQL without and with libhugetlbfs shows that performance increases by approximately 12%.
Reboot your server and run the test twice.
Throughput:
events/s (eps): 8604.3221
time elapsed: 300.0912s
total number of events: 2582080
The TPS is 8524 events/sec. You can also use perf stat during the run to look at the TLB refill counts.
perf stat -e l1d_tlb_refill,l1i_tlb_refill,l2d_tlb_refill -a -- sleep 10
The output will be similar to:
Performance counter stats for 'system wide':
815,254,864 l1d_tlb_refill
490,265,467 l1i_tlb_refill
422,887,362 l2d_tlb_refill
10.003289183 seconds time elapsed
Throughput:
events/s (eps): 8524.8307
time elapsed: 300.0878s
total number of events: 2558197
Reboot your server and run 2 more tests with libhugetlbfs enabled.
To enable hugepages, you need to run the following commands:
chown -R mysql.mysql /dev/hugepages
echo 40 > /proc/sys/vm/nr_hugepages
The first command gives permission to the mysql user to access hugepages (default is only root). The second command allocates 40 hugepages.
When the test is run you can check that hugepages are used:
cat /proc/meminfo
The output will show the number of free hugepages has decreased.
HugePages_Total: 40
HugePages_Free: 4
HugePages_Rsvd: 1
HugePages_Surp: 0
Hugepagesize: 2048 kB
Hugetlb: 81920 kB
In this case, MySQL used 36 huge pages (36*2M=72M).
The TPS is 9627 events/sec, a 12.9% increase compared to the first round without hugepages.
Throughput:
events/s (eps): 9627.5017
time elapsed: 300.0855s
total number of events: 2889073
The TPS is 9538 events/sec, a 11.9% increase compared to the second round without enabling hugepages.
The perf stat output shows TLB misses are significantly reduced:
perf stat -e l1d_tlb_refill,l1i_tlb_refill,l2d_tlb_refill -a -- sleep 10
The output will be similar to:
Performance counter stats for 'system wide':
688,157,786 l1d_tlb_refill
70,741,621 l1i_tlb_refill
254,054,393 l2d_tlb_refill
10.002128509 seconds time elapsed
Throughput:
events/s (eps): 9538.9346
time elapsed: 300.0847s
total number of events: 2862487
Building and running MySQL with libhugetlbfs provides increased performance.