Re: [PATCH] KVM: x86: lower default for halt_poll_ns

From	Paolo Bonzini <pbonzini@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH] KVM: x86: lower default for halt_poll_ns
Date	2017-05-16 19:00 +0200
Message-ID	<tHNZf-84e-3@gated-at.bofh.it> (permalink)
References	<txyRP-57S-7@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On 18/04/2017 12:41, Paolo Bonzini wrote:
> In some fio benchmarks, halt_poll_ns=400000 caused CPU utilization to
> increase heavily even in cases where the performance improvement was
> small.  In particular, bandwidth divided by CPU usage was as much as
> 60% lower.
> 
> To some extent this is the expected effect of the patch, and the
> additional CPU utilization is only visible when running the
> benchmarks.  However, halving the threshold also halves the extra
> CPU utilization (from +30-130% to +20-70%) and has no negative
> effect on performance.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Ping?

Paolo

> ---
>  arch/x86/include/asm/kvm_host.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 74ef58c8ff53..68d4a33da392 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -45,7 +45,7 @@
>  
>  #define KVM_PIO_PAGE_OFFSET 1
>  #define KVM_COALESCED_MMIO_PAGE_OFFSET 2
> -#define KVM_HALT_POLL_NS_DEFAULT 400000
> +#define KVM_HALT_POLL_NS_DEFAULT 200000
>  
>  #define KVM_IRQCHIP_NUM_PINS  KVM_IOAPIC_NUM_PINS
>  
>

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Re: [PATCH] KVM: x86: lower default for halt_poll_ns Paolo Bonzini <pbonzini@redhat.com> - 2017-05-16 19:00 +0200
  Re: [PATCH] KVM: x86: lower default for halt_poll_ns Radim Krčmář <rkrcmar@redhat.com> - 2017-05-16 22:50 +0200
    Re: [PATCH] KVM: x86: lower default for halt_poll_ns Paolo Bonzini <pbonzini@redhat.com> - 2017-05-17 09:00 +0200

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