Performance degrades after you enable the kernel option CONFIG_PARAVIRT_SPINLOCK - Alibaba Cloud Linux

CONFIG_PARAVIRT_SPINLOCK stands for paravirtualization layer for spinlocks. It is a Linux kernel option that is designed for virtualized environments that support paravirtualization. In the Alibaba Cloud Linux operating system, the kernel option CONFIG_PARAVIRT_SPINLOCK is disabled by default. If you are uncertain about how to resolve the kernel performance degradation, do not enable the CONFIG_PARAVIRT_SPINLOCK option. This topic describes the cause of and solution to the performance degradation that may occur if the kernel option CONFIG_PARAVIRT_SPINLOCK is enabled.

Problem description

After you enable the kernel option CONFIG_PARAVIRT_SPINLOCK on an Elastic Compute Service (ECS) instance that has multiple vCPUs, application performance is significantly affected if applications intensively compete for locks. For example, the capability of processing short-lived connections in the NGINX application is greatly reduced. You may observe performance degradation in applications.

Cause

Enabling the CONFIG_PARAVIRT_SPINLOCK option may introduce additional overheads and increase complexity in the spinlock mechanism of the kernel. As a result, the kernel performance degrades.

Note

A spinlock is a synchronization mechanism that prevents shared resources from being accessed by multiple threads or processes at the same time and helps ensure data consistency.

Solution

Run the following command to view the CONFIG_PARAVIRT_SPINLOCK setting in the kernel configuration file that is stored in the /boot directory:
```
grep CONFIG_PARAVIRT_SPINLOCK /boot/config-$(uname -r)
```
Check the command output to determine whether the CONFIG_PARAVIRT_SPINLOCK option is enabled for the kernel.
- CONFIG_PARAVIRT_SPINLOCKS=y: The CONFIG_PARAVIRT_SPINLOCK option is enabled.
- CONFIG_PARAVIRT_SPINLOCKS is not set: The CONFIG_PARAVIRT_SPINLOCK option is disabled.
(Conditionally required) If the CONFIG_PARAVIRT_SPINLOCK option is enabled, recompile and re-install the kernel and then disable the CONFIG_PARAVIRT_SPINLOCK option.
Note
Proceed with caution when you change the kernel configuration, because the operation involves the underlying layer and key components. In addition, this operation poses risks if you are unfamiliar with kernel compilation or installation. If you are uncertain about how to edit the kernel configuration file or compile and install the kernel, submit a ticket to contact Alibaba Cloud technical support.