| Message ID | 20240804-sparc-shr64-v1-1-25050968339a@protonmail.com |
|---|---|
| State | New |
| Headers | show |
| Series | sparc/vdso: Add helper function for 64-bit right shift on 32-bit target | expand |
On Sun, Aug 04 2024 at 10:39, Koakuma via wrote: > From: Koakuma <koachan@protonmail.com> > > Add helper function for 64-bit right shift on 32-bit target so that > clang does not emit a runtime library call. > > Signed-off-by: Koakuma <koachan@protonmail.com> > --- > Hi~ > > This adds a small function to do 64-bit right shifts for use in vDSO > code, needed so that clang does not emit a call to runtime library. > --- > arch/sparc/vdso/vclock_gettime.c | 8 ++++---- > include/vdso/math64.h | 28 ++++++++++++++++++++++++++++ > --- a/include/vdso/math64.h > +++ b/include/vdso/math64.h > @@ -21,6 +21,34 @@ __iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder) > return ret; > } > > +#if BITS_PER_LONG == 32 > +/* This is to prevent the compiler from emitting a call to __lshrdi3. */ > +static __always_inline u64 > +__shr64(u64 val, int amt) > +{ > + u32 mask = (1U << amt) - 1; > + u32 lo = val; > + u32 hi = val >> 32; > + u32 mi; > + > + if (amt >= 32) > + return hi >> (amt - 32); > + > + > + mi = (hi & mask) << (32 - amt); > + hi >>= amt; > + lo = (lo >> amt) | mi; > + > + return ((u64) hi) << 32 | lo; > +} > +#else > +static __always_inline u64 > +__shr64(u64 val, int amt) > +{ > + return val >> amt; > +} Why does this sparc'ism need to be in generic code? Thanks, tglx
Thomas Gleixner <tglx@linutronix.de> wrote:
> Why does this sparc'ism need to be in generic code?
Doesn't x86 also have a couple functions that live in math64.h anyway?
That's why I thought it is fine to put it in there...
In any case, though, I am open to moving the function to sparc directory,
if that is indeed the proper place for that function.
On Sun, Aug 04 2024 at 17:30, Koakuma wrote: > Thomas Gleixner <tglx@linutronix.de> wrote: >> Why does this sparc'ism need to be in generic code? > > Doesn't x86 also have a couple functions that live in math64.h anyway? No. Both functions are used in the generic lib/vdso/ code. > That's why I thought it is fine to put it in there... > > In any case, though, I am open to moving the function to sparc directory, > if that is indeed the proper place for that function. I think so as sparc is having it's own VDSO implementation and does not use the generic one. Thanks, tglx
Thomas Gleixner <tglx@linutronix.de> wrote: > I think so as sparc is having it's own VDSO implementation and does not > use the generic one. Understood. Lemme move the function to sparc code then.
diff --git a/arch/sparc/vdso/vclock_gettime.c b/arch/sparc/vdso/vclock_gettime.c index e794edde6755..c0251a632bdb 100644 --- a/arch/sparc/vdso/vclock_gettime.c +++ b/arch/sparc/vdso/vclock_gettime.c @@ -154,7 +154,7 @@ notrace static __always_inline int do_realtime(struct vvar_data *vvar, ts->tv_sec = vvar->wall_time_sec; ns = vvar->wall_time_snsec; ns += vgetsns(vvar); - ns >>= vvar->clock.shift; + ns = __shr64(ns, vvar->clock.shift); } while (unlikely(vvar_read_retry(vvar, seq))); ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns); @@ -174,7 +174,7 @@ notrace static __always_inline int do_realtime_stick(struct vvar_data *vvar, ts->tv_sec = vvar->wall_time_sec; ns = vvar->wall_time_snsec; ns += vgetsns_stick(vvar); - ns >>= vvar->clock.shift; + ns = __shr64(ns, vvar->clock.shift); } while (unlikely(vvar_read_retry(vvar, seq))); ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns); @@ -194,7 +194,7 @@ notrace static __always_inline int do_monotonic(struct vvar_data *vvar, ts->tv_sec = vvar->monotonic_time_sec; ns = vvar->monotonic_time_snsec; ns += vgetsns(vvar); - ns >>= vvar->clock.shift; + ns = __shr64(ns, vvar->clock.shift); } while (unlikely(vvar_read_retry(vvar, seq))); ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns); @@ -214,7 +214,7 @@ notrace static __always_inline int do_monotonic_stick(struct vvar_data *vvar, ts->tv_sec = vvar->monotonic_time_sec; ns = vvar->monotonic_time_snsec; ns += vgetsns_stick(vvar); - ns >>= vvar->clock.shift; + ns = __shr64(ns, vvar->clock.shift); } while (unlikely(vvar_read_retry(vvar, seq))); ts->tv_sec += __iter_div_u64_rem(ns, NSEC_PER_SEC, &ns); diff --git a/include/vdso/math64.h b/include/vdso/math64.h index 22ae212f8b28..771d84faa8d7 100644 --- a/include/vdso/math64.h +++ b/include/vdso/math64.h @@ -21,6 +21,34 @@ __iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder) return ret; } +#if BITS_PER_LONG == 32 +/* This is to prevent the compiler from emitting a call to __lshrdi3. */ +static __always_inline u64 +__shr64(u64 val, int amt) +{ + u32 mask = (1U << amt) - 1; + u32 lo = val; + u32 hi = val >> 32; + u32 mi; + + if (amt >= 32) + return hi >> (amt - 32); + + + mi = (hi & mask) << (32 - amt); + hi >>= amt; + lo = (lo >> amt) | mi; + + return ((u64) hi) << 32 | lo; +} +#else +static __always_inline u64 +__shr64(u64 val, int amt) +{ + return val >> amt; +} +#endif /* BITS_PER_LONG == 32 */ + #if defined(CONFIG_ARCH_SUPPORTS_INT128) && defined(__SIZEOF_INT128__) #ifndef mul_u64_u32_add_u64_shr