Re: [RFC] VMX CR3 cache

[Gerd Hoffmann <kraxel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

Marcelo Tosatti wrote:
> Hi,
> 
> The CR3 cache feature of VMX CPU's does not seem to increase
> context switch performance significantly as it did in the original
> implementation (http://lkml.org/lkml/2007/1/5/205).
> 
> The following is similar to the original, but it also caches roots for
> 4-level pagetables on x86-64, and clearing the cache is only performed
> in zap_page() instead of on every pagefault.

Hmm, what kvm version is this against?  latest git I guess?  After
applying to kvm-60 (and fixing up some trivial rejects) it doesn't build.

> Nowhere near the results achieved earlier (and kernel compilation and
> httperf seems slightly slower, probably due to paravirt overhead).

Even if it it doesn't help much on native:  With xenner it probably
gives a nice speedup especially on 64 bit where each guest syscall
involves a cr3 switch (not benchmarked yet though).

>  #ifdef __KERNEL__
>  #include <asm/processor.h>
>  
> -#define KVM_PARA_FEATURES (1UL << KVM_FEATURE_NOP_IO_DELAY)
> +#define KVM_PARA_FEATURES ((1UL << KVM_FEATURE_NOP_IO_DELAY) | 	\
> +			   (1UL << KVM_FEATURE_CR3_CACHE))
> +
> +#define KVM_MSR_SET_CR3_CACHE 0x87655678
> +
> +#define KVM_CR3_CACHE_SIZE 4
> +
> +struct kvm_cr3_cache_entry {
> +	u64 guest_cr3;
> +	u64 host_cr3;
> +};
> +
> +struct kvm_cr3_cache {
> +	struct kvm_cr3_cache_entry entry[KVM_CR3_CACHE_SIZE];
> +	u32 max_idx;
> +};

Can you move the structs out of #ifdef __KERNEL__ please?

thanks,
  Gerd



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