From: Alexander Lobakin <alexandr.lobakin@intel.com>
To: Yury Norov <yury.norov@gmail.com>
Cc: Alexander Lobakin <alexandr.lobakin@intel.com>,
Arnd Bergmann <arnd@arndb.de>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Mark Rutland <mark.rutland@arm.com>,
Matt Turner <mattst88@gmail.com>, Brian Cain <bcain@quicinc.com>,
Geert Uytterhoeven <geert@linux-m68k.org>,
Yoshinori Sato <ysato@users.sourceforge.jp>,
Rich Felker <dalias@libc.org>,
"David S. Miller" <davem@davemloft.net>,
Kees Cook <keescook@chromium.org>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Marco Elver <elver@google.com>, Borislav Petkov <bp@suse.de>,
Tony Luck <tony.luck@intel.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-alpha@vger.kernel.org, linux-hexagon@vger.kernel.org,
linux-ia64@vger.kernel.org, linux-m68k@lists.linux-m68k.org,
linux-sh@vger.kernel.org, sparclinux@vger.kernel.org,
linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 4/6] bitops: define const_*() versions of the non-atomics
Date: Wed, 15 Jun 2022 15:55:06 +0200 [thread overview]
Message-ID: <20220615135506.1264880-1-alexandr.lobakin@intel.com> (raw)
In-Reply-To: <YqlKpwjQ4Hu+Lr8u@yury-laptop>
From: Yury Norov <yury.norov@gmail.com>
Date: Tue, 14 Jun 2022 19:57:43 -0700
> On Fri, Jun 10, 2022 at 01:34:25PM +0200, Alexander Lobakin wrote:
> > Define const_*() variants of the non-atomic bitops to be used when
> > the input arguments are compile-time constants, so that the compiler
> > will be always to resolve those to compile-time constants as well.
>
> will be always able?
Right, ooops.
>
> > Those are mostly direct aliases for generic_*() with one exception
> > for const_test_bit(): the original one is declared atomic-safe and
> > thus doesn't discard the `volatile` qualifier, so in order to let
> > optimize the code, define it separately disregarding the qualifier.
> > Add them to the compile-time type checks as well just in case.
> >
> > Suggested-by: Marco Elver <elver@google.com>
> > Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com>
> > ---
> > .../asm-generic/bitops/generic-non-atomic.h | 31 +++++++++++++++++++
> > include/linux/bitops.h | 3 +-
> > 2 files changed, 33 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/asm-generic/bitops/generic-non-atomic.h b/include/asm-generic/bitops/generic-non-atomic.h
> > index 3ce0fa0ab35f..9a77babfff35 100644
> > --- a/include/asm-generic/bitops/generic-non-atomic.h
> > +++ b/include/asm-generic/bitops/generic-non-atomic.h
> > @@ -121,4 +121,35 @@ generic_test_bit(unsigned long nr, const volatile unsigned long *addr)
> > return 1UL & (addr[BIT_WORD(nr)] >> (nr & (BITS_PER_LONG-1)));
> > }
> >
> > +/*
> > + * const_*() definitions provide good compile-time optimizations when
> > + * the passed arguments can be resolved at compile time.
> > + */
> > +#define const___set_bit generic___set_bit
> > +#define const___clear_bit generic___clear_bit
> > +#define const___change_bit generic___change_bit
> > +#define const___test_and_set_bit generic___test_and_set_bit
> > +#define const___test_and_clear_bit generic___test_and_clear_bit
> > +#define const___test_and_change_bit generic___test_and_change_bit
> > +
> > +/**
> > + * const_test_bit - Determine whether a bit is set
> > + * @nr: bit number to test
> > + * @addr: Address to start counting from
> > + *
> > + * A version of generic_test_bit() which discards the `volatile` qualifier to
> > + * allow the compiler to optimize code harder. Non-atomic and to be used only
> > + * for testing compile-time constants, e.g. from the corresponding macro, or
> > + * when you really know what you are doing.
>
> Not sure I understand the last sentence... Can you please rephrase?
I basically want to tell that there potentinally might be cases for
using those outside of the actual macros from 6/6. But it might be
redundant at all to mention this.
>
> > + */
> > +static __always_inline bool
> > +const_test_bit(unsigned long nr, const volatile unsigned long *addr)
> > +{
> > + const unsigned long *p = (const unsigned long *)addr + BIT_WORD(nr);
> > + unsigned long mask = BIT_MASK(nr);
> > + unsigned long val = *p;
> > +
> > + return !!(val & mask);
> > +}
> > +
> > #endif /* __ASM_GENERIC_BITOPS_GENERIC_NON_ATOMIC_H */
> > diff --git a/include/linux/bitops.h b/include/linux/bitops.h
> > index 87087454a288..51c22b8667b4 100644
> > --- a/include/linux/bitops.h
> > +++ b/include/linux/bitops.h
> > @@ -36,7 +36,8 @@ extern unsigned long __sw_hweight64(__u64 w);
> >
> > /* Check that the bitops prototypes are sane */
> > #define __check_bitop_pr(name) \
> > - static_assert(__same_type(arch_##name, generic_##name) && \
> > + static_assert(__same_type(const_##name, generic_##name) && \
> > + __same_type(arch_##name, generic_##name) && \
> > __same_type(name, generic_##name))
> >
> > __check_bitop_pr(__set_bit);
> > --
> > 2.36.1
Thanks,
Olek
next prev parent reply other threads:[~2022-06-15 13:57 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-10 11:34 [PATCH v2 0/6] bitops: let optimize out non-atomic bitops on compile-time constants Alexander Lobakin
2022-06-10 11:34 ` [PATCH v2 1/6] ia64, processor: fix -Wincompatible-pointer-types in ia64_get_irr() Alexander Lobakin
2022-06-10 12:18 ` David Laight
2022-06-10 13:46 ` Andy Shevchenko
2022-06-15 2:59 ` Yury Norov
2022-06-10 11:34 ` [PATCH v2 2/6] bitops: always define asm-generic non-atomic bitops Alexander Lobakin
2022-06-10 13:50 ` Andy Shevchenko
2022-06-10 16:02 ` Luck, Tony
2022-06-10 16:32 ` Marco Elver
2022-06-13 14:19 ` Alexander Lobakin
2022-06-13 14:33 ` Marco Elver
2022-06-15 2:47 ` Yury Norov
2022-06-15 7:46 ` Marco Elver
2022-06-13 16:26 ` Luck, Tony
2022-06-13 21:29 ` David Laight
2022-06-10 11:34 ` [PATCH v2 3/6] bitops: unify non-atomic bitops prototypes across architectures Alexander Lobakin
2022-06-10 11:34 ` [PATCH v2 4/6] bitops: define const_*() versions of the non-atomics Alexander Lobakin
2022-06-10 13:56 ` Andy Shevchenko
2022-06-13 14:30 ` Alexander Lobakin
2022-06-15 2:57 ` Yury Norov
2022-06-15 13:55 ` Alexander Lobakin [this message]
2022-06-15 15:52 ` David Laight
2022-06-10 11:34 ` [PATCH v2 5/6] bitops: wrap non-atomic bitops with a transparent macro Alexander Lobakin
2022-06-10 11:34 ` [PATCH v2 6/6] bitops: let optimize out non-atomic bitops on compile-time constants Alexander Lobakin
2022-06-15 3:26 ` Yury Norov
2022-06-15 14:00 ` Alexander Lobakin
2022-06-13 7:35 ` [PATCH v2 0/6] " Geert Uytterhoeven
2022-06-13 14:26 ` Alexander Lobakin
2022-06-13 15:22 ` Geert Uytterhoeven
2022-06-15 14:17 ` Alexander Lobakin
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