| Message ID | 5613A531.5050506@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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 kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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