Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1240381

Re: [PATCH 04/12] KVM: x86: Replace call-back set_tsc_khz() with a common function

From Haozhong Zhang <haozhong.zhang@intel.com>
Newsgroups linux.kernel
Subject Re: [PATCH 04/12] KVM: x86: Replace call-back set_tsc_khz() with a common function
Date 2015-10-06 13:40 +0200
Message-ID <qgyL7-4TN-1@gated-at.bofh.it> (permalink)
References <qdzkm-4Rn-5@gated-at.bofh.it> <qdzu2-52B-13@gated-at.bofh.it> <qgk5r-kd-1@gated-at.bofh.it> <qgrJD-3gz-1@gated-at.bofh.it> <qgxYK-3JK-13@gated-at.bofh.it>
Organization linux.* mail to news gateway

Show all headers | View raw

On Tue, Oct 06, 2015 at 12:40:49PM +0200, Paolo Bonzini wrote:
> 
> 
> On 06/10/2015 06:06, Haozhong Zhang wrote:
> > Alternatively, it's also possible to follow David's comment to use
> > divq on x86_64 to keep both precision and safety. On i386, it just
> > falls back to above truncating approach.
> 
> khz is just 32 bits, so we can do a 96/32 division.  And because this is
> a slow path, we can code a generic u64*u32/u32 function and use it to do
> (1 << kvm_tsc_scaling_ratio_frac_bits) * khz / tsc_khz:
>

This is much better! Thanks Paolo! I'll use this mul_u64_u32_shr() in
the next version.

> diff --git a/include/linux/math64.h b/include/linux/math64.h
> index c45c089bfdac..5b70af4fa386 100644
> --- a/include/linux/math64.h
> +++ b/include/linux/math64.h
> @@ -142,6 +142,13 @@ static inline u64 mul_u64_u32_shr(u64 a, u32 mul,
> unsigned int shift)
>  }
>  #endif /* mul_u64_u32_shr */
> 
> +#ifndef mul_u64_u32_div
> +static inline u64 mul_u64_u32_div(u64 x, u32 num, u32 den)
> +{
> +	return (u64)(((unsigned __int128)a * mul) / den);
> +}
> +#endif
> +
>  #else
> 
>  #ifndef mul_u64_u32_shr
> @@ -161,6 +168,35 @@ static inline u64 mul_u64_u32_shr(u64 a, u32 mul,
> unsigned int shift)
>  }
>  #endif /* mul_u64_u32_shr */
> 
> +#ifndef mul_u64_u32_div
> +static inline u64 mul_u64_u32_div(u64 a, u32 num, u32 den)
> +{
> +	union {
> +		u64 ll;
> +		struct {
> +#ifdef __BIG_ENDIAN
> +			u32 high, low;
> +#else
> +			u32 low, high;
> +#endif
> +		} l;
> +	} u, rl, rh;
> +
> +	u.ll = a;
> +	rl.ll = (u64)u.l.low * num;
> +	rh.ll = (u64)u.l.high * num + rl.l.high;
> +
> +	/* Bits 32-63 of the result will be in rh.l.low.  */
> +	rl.l.high = do_div(rh.ll, den);
> +
> +	/* Bits 0-31 of the result will be in rl.l.low.  */
> +	do_div(rl.ll, den);
> +
> +	rl.l.high = rh.l.low;
> +	return rl.ll;
> +}
> +#endif
> +
>  #endif
> 
>  #endif /* _LINUX_MATH64_H */
> --
> To unsubscribe from this list: send the line "unsubscribe kvm" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH 00/12] KVM: x86: add support for VMX TSC scaling Haozhong Zhang <haozhong.zhang@intel.com> - 2015-09-28 07:40 +0200
  [PATCH 07/12] KVM: x86: Move TSC scaling logic out of call-back read_l1_tsc() Haozhong Zhang <haozhong.zhang@intel.com> - 2015-09-28 07:40 +0200
  [PATCH 11/12] KVM: VMX: Use a scaled host TSC for guest readings of MSR_IA32_TSC Haozhong Zhang <haozhong.zhang@intel.com> - 2015-09-28 07:40 +0200
  [PATCH 06/12] KVM: x86: Move TSC scaling logic out of call-back adjust_tsc_offset() Haozhong Zhang <haozhong.zhang@intel.com> - 2015-09-28 07:40 +0200
    Re: [PATCH 06/12] KVM: x86: Move TSC scaling logic out of call-back  adjust_tsc_offset() Paolo Bonzini <pbonzini@redhat.com> - 2015-09-28 22:20 +0200
      Re: [PATCH 06/12] KVM: x86: Move TSC scaling logic out of call-back  adjust_tsc_offset() Haozhong Zhang <haozhong.zhang@intel.com> - 2015-09-29 03:50 +0200
  [PATCH 01/12] KVM: x86: Collect information for setting TSC scaling ratio Haozhong Zhang <haozhong.zhang@intel.com> - 2015-09-28 07:40 +0200
    Re: [PATCH 01/12] KVM: x86: Collect information for setting TSC  scaling ratio Eric Northup <digitaleric@google.com> - 2015-09-29 05:30 +0200
      Re: [PATCH 01/12] KVM: x86: Collect information for setting TSC  scaling ratio Haozhong Zhang <haozhong.zhang@intel.com> - 2015-09-29 06:10 +0200
  [PATCH 02/12] KVM: x86: Add a common TSC scaling ratio field in kvm_vcpu_arch Haozhong Zhang <haozhong.zhang@intel.com> - 2015-09-28 07:50 +0200
    Re: [PATCH 02/12] KVM: x86: Add a common TSC scaling ratio field in  kvm_vcpu_arch Radim Krčmář <rkrcmar@redhat.com> - 2015-10-05 21:30 +0200
      Re: [PATCH 02/12] KVM: x86: Add a common TSC scaling ratio field in  kvm_vcpu_arch Haozhong Zhang <haozhong.zhang@intel.com> - 2015-10-06 04:00 +0200
  [PATCH 08/12] KVM: x86: Use the correct vcpu's TSC rate to compute time scale Haozhong Zhang <haozhong.zhang@intel.com> - 2015-09-28 07:50 +0200
    Re: [PATCH 08/12] KVM: x86: Use the correct vcpu's TSC rate to  compute time scale Radim Krčmář <rkrcmar@redhat.com> - 2015-10-05 22:20 +0200
  [PATCH 05/12] KVM: x86: Replace call-back compute_tsc_offset() with a common function Haozhong Zhang <haozhong.zhang@intel.com> - 2015-09-28 07:50 +0200
  [PATCH 03/12] KVM: x86: Add a common TSC scaling function Haozhong Zhang <haozhong.zhang@intel.com> - 2015-09-28 07:50 +0200
    Re: [PATCH 03/12] KVM: x86: Add a common TSC scaling function Paolo Bonzini <pbonzini@redhat.com> - 2015-09-28 22:20 +0200
      Re: [PATCH 03/12] KVM: x86: Add a common TSC scaling function Haozhong Zhang <haozhong.zhang@intel.com> - 2015-09-29 04:00 +0200
  [PATCH 10/12] KVM: VMX: Setup TSC scaling ratio when a vcpu is loaded Haozhong Zhang <haozhong.zhang@intel.com> - 2015-09-28 07:50 +0200
  [PATCH 04/12] KVM: x86: Replace call-back set_tsc_khz() with a common function Haozhong Zhang <haozhong.zhang@intel.com> - 2015-09-28 07:50 +0200
    Re: [PATCH 04/12] KVM: x86: Replace call-back set_tsc_khz() with a  common function Haozhong Zhang <haozhong.zhang@intel.com> - 2015-09-29 05:50 +0200
    Re: [PATCH 04/12] KVM: x86: Replace call-back set_tsc_khz() with a  common function Radim Krčmář <rkrcmar@redhat.com> - 2015-10-05 22:00 +0200
      Re: [PATCH 04/12] KVM: x86: Replace call-back set_tsc_khz() with a  common function David Matlack <dmatlack@google.com> - 2015-10-05 22:50 +0200
      Re: [PATCH 04/12] KVM: x86: Replace call-back set_tsc_khz() with a  common function Haozhong Zhang <haozhong.zhang@intel.com> - 2015-10-06 06:10 +0200
        Re: [PATCH 04/12] KVM: x86: Replace call-back set_tsc_khz() with a  common function Paolo Bonzini <pbonzini@redhat.com> - 2015-10-06 12:50 +0200
          Re: [PATCH 04/12] KVM: x86: Replace call-back set_tsc_khz() with a  common function Haozhong Zhang <haozhong.zhang@intel.com> - 2015-10-06 13:40 +0200
  Re: [PATCH 00/12] KVM: x86: add support for VMX TSC scaling Haozhong Zhang <haozhong.zhang@intel.com> - 2015-09-29 06:10 +0200
  Re: [PATCH 00/12] KVM: x86: add support for VMX TSC scaling Eric Northup <digitaleric@google.com> - 2015-09-29 06:10 +0200

csiph-web