Messages in this thread | | | Date | Mon, 27 Jun 2022 09:25:54 -0400 | Subject | Re: [PATCH v2] x86/paravirt: useless assignment instructions cause Unixbench full core performance degradation | From | Waiman Long <> |
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On 6/27/22 01:54, Guo Hui wrote: > Thank you very much Longman, my patch is as you said, only disable > node_cpu on X86, enable node_cpu on arm64, powerpc, s390 architectures; > the code is in file arch/x86/kernel/paravirt-spinlocks.c: > DECLARE_STATIC_KEY_FALSE(preemted_key); > static_branch_enable(&preemted_key); > > the default value of preemted_key is false and the if conditional > statement is reversed, > the code is in file kernel/locking/osq_lock.c: > DEFINE_STATIC_KEY_FALSE(preemted_key); > > static inline int node_cpu(struct optimistic_spin_node *node) > { > int cpu = 0; > > if (!static_branch_unlikely(&preemted_key)) > cpu = node->cpu - 1; > > return cpu; > } > > In this way, only one nop instruction is added to architectures arm64, > powerpc and s390, including virtual machines, without any other changes.
You are right. I am probably too tired last night to read the patch more carefully.
Cheers, Longman
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