In this section, you establish a baseline configuration before applying advanced techniques to tune the performance of Tomcat-based network workloads on an Arm Neoverse bare-metal instance.
To avoid running out of file descriptors under load, raise the file‑descriptor limit on both the server and the client:
ulimit -n 65535
This baseline includes:
If you are using a cloud image (for example, AWS) with non-default kernel parameters, align IOMMU settings with the Ubuntu defaults: iommu.strict=1 and iommu.passthrough=0.
Edit GRUB and add (or update) GRUB_CMDLINE_LINUX:
sudo vi /etc/default/grub
Add or update the line to include:
GRUB_CMDLINE_LINUX="iommu.strict=1 iommu.passthrough=0"
Update GRUB and reboot to apply the settings:
sudo update-grub && sudo reboot
Verify that the default settings have been successfully applied:
sudo dmesg | grep iommu
You should see that under the default configuration, iommu.strict is enabled, and iommu.passthrough is disabled:
[ 0.877401] iommu: Default domain type: Translated (set via kernel command line)
[ 0.877404] iommu: DMA domain TLB invalidation policy: strict mode (set via kernel command line)
...
To mirror a typical Tomcat deployment and simplify tuning, keep 8 CPU cores online and set the remaining cores offline. Adjust the CPU range to match your instance. The example below assumes 192 CPUs (as on AWS c8g.metal-48xl).
Set CPUs 8–191 offline:
for no in {8..191}; do sudo bash -c "echo 0 > /sys/devices/system/cpu/cpu${no}/online"; done
Confirm that CPUs 0–7 are online and the rest are offline:
lscpu
Example output:
Architecture: aarch64
CPU op-mode(s): 64-bit
Byte Order: Little Endian
CPU(s): 192
On-line CPU(s) list: 0-7
Off-line CPU(s) list: 8-191
Vendor ID: ARM
Model name: Neoverse-V2
...
Restart Tomcat on the Arm instance:
~/apache-tomcat-11.0.10/bin/shutdown.sh 2>/dev/null
ulimit -n 65535 && ~/apache-tomcat-11.0.10/bin/startup.sh
From your x86_64 benchmarking client, run wrk2 (replace <tomcat_ip> with the server’s IP):
ulimit -n 65535 && wrk -c1280 -t128 -R500000 -d60 http://<tomcat_ip>:8080/examples/servlets/servlet/HelloWorldExample
Example result:
Thread Stats Avg Stdev Max +/- Stdev
Latency 16.76s 6.59s 27.56s 56.98%
Req/Sec 1.97k 165.05 2.33k 89.90%
14680146 requests in 1.00m, 7.62GB read
Socket errors: connect 1264, read 0, write 0, timeout 1748
Requests/sec: 244449.62
Transfer/sec: 129.90MB
Disabling access logs removes I/O overhead during benchmarking.
Edit server.xml and comment out (or remove) the org.apache.catalina.valves.AccessLogValve block:
vi ~/apache-tomcat-11.0.10/conf/server.xml
<!--
<Valve className="org.apache.catalina.valves.AccessLogValve" directory="logs"
prefix="localhost_access_log" suffix=".txt"
pattern="%h %l %u %t "%r" %s %b" />
-->
Restart Tomcat:
~/apache-tomcat-11.0.10/bin/shutdown.sh 2>/dev/null
ulimit -n 65535 && ~/apache-tomcat-11.0.10/bin/startup.sh
Re-run wrk2:
ulimit -n 65535 && wrk -c1280 -t128 -R500000 -d60 http://<tomcat_ip>:8080/examples/servlets/servlet/HelloWorldExample
Example result:
Thread Stats Avg Stdev Max +/- Stdev
Latency 16.16s 6.45s 28.26s 57.85%
Req/Sec 2.16k 5.91 2.17k 77.50%
16291136 requests in 1.00m, 8.45GB read
Socket errors: connect 0, read 0, write 0, timeout 75
Requests/sec: 271675.12
Transfer/sec: 144.36MB
To minimize contention and context switching, align Tomcat’s CPU‑intensive thread count with available CPU cores.
While wrk2 is running, identify CPU‑intensive Tomcat threads:
top -H -p "$(pgrep -n java)"
Example output:
top - 08:57:29 up 20 min, 1 user, load average: 4.17, 2.35, 1.22
Threads: 231 total, 8 running, 223 sleeping, 0 stopped, 0 zombie
%Cpu(s): 31.7 us, 20.2 sy, 0.0 ni, 31.0 id, 0.0 wa, 0.0 hi, 17.2 si, 0.0 st
MiB Mem : 386127.8 total, 380676.0 free, 4040.7 used, 2801.1 buff/cache
MiB Swap: 0.0 total, 0.0 free, 0.0 used. 382087.0 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
4677 ubuntu 20 0 36.0g 1.4g 24452 R 89.0 0.4 1:18.71 http-nio-8080-P
4685 ubuntu 20 0 36.0g 1.4g 24452 R 4.7 0.4 0:04.42 http-nio-8080-A
4893 ubuntu 20 0 36.0g 1.4g 24452 S 3.3 0.4 0:00.60 http-nio-8080-e
4963 ubuntu 20 0 36.0g 1.4g 24452 S 3.3 0.4 0:00.66 http-nio-8080-e
4924 ubuntu 20 0 36.0g 1.4g 24452 S 3.0 0.4 0:00.59 http-nio-8080-e
4955 ubuntu 20 0 36.0g 1.4g 24452 S 3.0 0.4 0:00.60 http-nio-8080-e
5061 ubuntu 20 0 36.0g 1.4g 24452 S 3.0 0.4 0:00.61 http-nio-8080-e
4895 ubuntu 20 0 36.0g 1.4g 24452 S 2.7 0.4 0:00.58 http-nio-8080-e
4907 ubuntu 20 0 36.0g 1.4g 24452 S 2.7 0.4 0:00.59 http-nio-8080-e
4940 ubuntu 20 0 36.0g 1.4g 24452 S 2.7 0.4 0:00.58 http-nio-8080-e
4946 ubuntu 20 0 36.0g 1.4g 24452 S 2.7 0.4 0:00.59 http-nio-8080-e
4956 ubuntu 20 0 36.0g 1.4g 24452 S 2.7 0.4 0:00.65 http-nio-8080-e
4959 ubuntu 20 0 36.0g 1.4g 24452 S 2.7 0.4 0:00.59 http-nio-8080-e
4960 ubuntu 20 0 36.0g 1.4g 24452 R 2.7 0.4 0:00.60 http-nio-8080-e
4962 ubuntu 20 0 36.0g 1.4g 24452 S 2.7 0.4 0:00.57 http-nio-8080-e
4982 ubuntu 20 0 36.0g 1.4g 24452 S 2.7 0.4 0:00.63 http-nio-8080-e
4983 ubuntu 20 0 36.0g 1.4g 24452 S 2.7 0.4 0:00.58 http-nio-8080-e
4996 ubuntu 20 0 36.0g 1.4g 24452 S 2.7 0.4 0:00.60 http-nio-8080-e
5033 ubuntu 20 0 36.0g 1.4g 24452 S 2.7 0.4 0:00.59 http-nio-8080-e
5036 ubuntu 20 0 36.0g 1.4g 24452 S 2.7 0.4 0:00.66 http-nio-8080-e
5056 ubuntu 20 0 36.0g 1.4g 24452 S 2.7 0.4 0:00.61 http-nio-8080-e
5065 ubuntu 20 0 36.0g 1.4g 24452 S 2.7 0.4 0:00.56 http-nio-8080-e
5068 ubuntu 20 0 36.0g 1.4g 24452 S 2.7 0.4 0:00.61 http-nio-8080-e
5070 ubuntu 20 0 36.0g 1.4g 24452 S 2.7 0.4 0:00.60 http-nio-8080-e
5071 ubuntu 20 0 36.0g 1.4g 24452 S 2.7 0.4 0:00.61 http-nio-8080-e
...
You’ll typically see http-nio-8080-e and http-nio-8080-P threads as CPU-intensive. Because the http-nio-8080-P thread count is fixed at 1 (in current Tomcat releases), and you have 8 online CPU cores, set http-nio-8080-e to 7.
Edit server.xml and update the HTTP connector to set the worker thread counts and connection limits:
vi ~/apache-tomcat-11.0.10/conf/server.xml
Replace the existing connector:
<!-- Before -->
<Connector port="8080" protocol="HTTP/1.1"
connectionTimeout="20000"
redirectPort="8443" />
With the tuned settings:
<!-- After -->
<Connector port="8080" protocol="HTTP/1.1"
connectionTimeout="20000"
redirectPort="8443"
minSpareThreads="7"
maxThreads="7"
maxKeepAliveRequests="500000"
maxConnections="100000"
/>
Restart Tomcat and re-run wrk2:
~/apache-tomcat-11.0.10/bin/shutdown.sh 2>/dev/null
ulimit -n 65535 && ~/apache-tomcat-11.0.10/bin/startup.sh
ulimit -n 65535 && wrk -c1280 -t128 -R500000 -d60 http://<tomcat_ip>:8080/examples/servlets/servlet/HelloWorldExample
Example result:
Thread Stats Avg Stdev Max +/- Stdev
Latency 10.26s 4.55s 19.81s 62.51%
Req/Sec 2.86k 89.49 3.51k 77.06%
21458421 requests in 1.00m, 11.13GB read
Requests/sec: 357835.75
Transfer/sec: 190.08MB
With a solid baseline in place, you’re ready to proceed to NIC queue tuning, NUMA locality optimization, and IOMMU exploration in the next sections.