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Linux 6.15 Fix Merged For Sizable Performance Regression On Newer AMD CPUs
At the end of April I reported on a significant performance regression affecting newer AMD CPUs and was bisected to a change in the AMD SRSO mitigation handling for Zen 4/5 processors with the Linux 6.15 kernel
The fix for that significant performance regression was merged today ahead of the imminent Linux 6.15-rc6 release. The involved performance costs ended up being more significant than the upstream kernel developers from AMD and Google realized at the time. Use a dedicated spinlock and counter instead of hooking virtualization enablement, as changing the behavior of kvm.enable_virt_at_load based on SRSO_BP_SPEC_REDUCE is painful, and has its own drawbacks, e.g. could result in performance issues for flows that are sensitive to VM creation latency.
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