Help Center/ Huawei Cloud EulerOS/ User Guide/ HCE-specific System Startup Parameters
Updated on 2025-07-21 GMT+08:00
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HCE-specific System Startup Parameters

Compared with CentOS 8, HCE has some custom system startup parameters.

nohz

In versions earlier than Linux kernel 2.6.17, the Linux kernel sets a periodic clock interrupt for each CPU. The kernel processes some cron jobs during the interruption, such as thread scheduling. As a result, a lot of clock interrupts are generated even if a CPU does not need a timer, causing resource wastes. nohz is introduced into Linux kernel 2.6.17. It makes clock interrupts configurable to reduce clock interrupts on idle CPUs.

nohz can help improve CPU energy efficiency but it may have a negative impact on load balancing. Enabling nohz in some cases will deteriorate performance. So, you are advised to disable nohz by default. You can add nohz=off to system startup parameters and restart the system to disable it.

nohz has a positive impact on performance in some special cases, for example, when multiple threads concurrently read /proc/cpuinfo.

mitigations

In January 2018, Google Project Zero disclosed that modern processors have security vulnerabilities Spectre and Meltdown, which exist in most mainstream processors (including Intel, AMD, and Arm architectures). These vulnerabilities were fixed in all mainstream operating systems, for example, Linux. mitigations is used to control whether to enable fixing these CPU vulnerabilities.

Vulnerability fixing depends on speculative execution and out-of-order execution features of processor hardware. These features are critical for improving the performance of modern processors. So, CPU vulnerability fixing will deteriorate performance. In some extreme cases, the performance deterioration even exceeds 50%. Additionally, software fixing can only alleviate but cannot solve the vulnerability problem. You are advised to disable mitigations by default. You can add mitigations=off to system startup parameters and restart the system to disable it.