A Linux kernel 6.13-rc3 update includes a change that eliminates a performance regression in the KVM hypervisor, related to the slow processing of CPUID calls on newer CPUs. For instance, on Intel's Emerald Rapids CPUs, CPUID operations are performed 3-4 times slower than on Intel's Skylake CPUs. This issue caused a drop in KVM hypervisor performance, which uses CPUID during the saving and restoring of the processor state with each control handover to the virtual machine when nested virtualization is used. To address this problem, a streamlined patch has been accepted into the 6.13 kernel branch, which allows for up to a 40% reduction in operation time even on Skylake CPUs, thanks to CPUID caching. A full version of the patch, further improving performance, will be presented in kernel 6.14.
Additionally, there has been a discussion in the Linux kernel developers' mailing list about ending support for 32-bit systems in the hypervisor. KVMInitially, a patch was proposed for the kernel that would remove KVM virtualization support on the x86-32 platform. Concerns were raised in response that support for x86-32 might be useful for testing the host mode's functionality on 32-bit systems in general, as there are still three other 32-bit architectures supported in KVM besides x86-32 in the kernel. In response, another patch was presented, this time removing support for all 32-bit systems from KVM.
The desire to remove support for 32-bit systems is explained by the fact that even on common 32-bit ARM processors, such as the ARM Cortex A7, virtualization has not developed or been utilized. virtuális gépekhez The use of 32-bit ARM systems was so rare that support for these systems in KVM was removed in 2020 without any objections. It is noted that for the remaining 32-bit systems, changes will only affect exotic platforms that have long been unused in practice or were never popular. Among the processors affected by the patch are: Intel Core Duo/Silverthorne, PowerPC e300/e500/e600, and MIPS P5600. The patch has been published as RFC, meaning it is open for discussion.
Forrás: opennet.ru
