From: Arnd Bergmann <arnd@kernel.org>
To: Guo Ren <guoren@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Marco Elver <elver@google.com>, Arnd Bergmann <arnd@arndb.de>,
Russell King <linux@armlinux.org.uk>,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Darren Hart <dvhart@infradead.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Davidlohr Bueso <dave@stgolabs.net>,
Elena Reshetova <elena.reshetova@intel.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
linux-csky@vger.kernel.org,
sparclinux <sparclinux@vger.kernel.org>,
"David S. Miller" <davem@davemloft.net>
Subject: Re: [PATCH 1/2] futex: mark futex_detect_cmpxchg() as 'noinline'
Date: Tue, 15 Dec 2020 12:26:10 +0100 [thread overview]
Message-ID: <CAK8P3a3+WaQNyJ6Za2qfu6=0mBgU1hApnRXrdp1b1=P7wwyRUg@mail.gmail.com> (raw)
In-Reply-To: <CAJF2gTRLEbBfZJ7Y6UNOMq-cwG5OYRW=+8Pfauz6v6R8ntBjYA@mail.gmail.com>
On Tue, Dec 15, 2020 at 7:09 AM Guo Ren <guoren@kernel.org> wrote:
> On Mon, Dec 14, 2020 at 9:15 PM Arnd Bergmann <arnd@kernel.org> wrote:
> > I had a look at what other architectures always implement
> > futex_atomic_cmpxchg_inatomic() or can use the asm-generic non-SMP version,
> > and I found that it's pretty much all of them, the odd ones being just sparc32
> > and csky, which use asm-generic/futex.h but do have an SMP option,
> > as well as xtensa
> >
> > I would guess that for csky, this is a mistake, as the architecture is fairly
> > new and should be able to implement it. Not sure about sparc32.
>
> The c610, c807, c810 don't support SMP, so futex_cmpxchg_enabled = 1
> with asm-generic's implementation.
> For c860, there is no HAVE_FUTEX_CMPXCHG and cmpxchg_inatomic/inuser
> implementation, so futex_cmpxchg_enabled = 0.
>
> Thx for point it out, we'll implement cmpxchg_inatomic/inuser for C860
> and still use asm-generic for non-smp CPUs.
Sounds good to me.
With that, I would suggest we actually remove the -ENOSYS fallback
for arch_futex_atomic_op_inuser() and futex_atomic_cmpxchg_inatomic()
in asm-generic/futex.h as well as the HAVE_FUTEX_CMPXCHG Kconfig
symbol, plus these additional fixups:
- for xtensa and mips configurations without ll/sc, fall back to the
asm-generic version. These are all uniprocessor, while the
corresponding SMP machines have a working
arch_futex_atomic_op_inuser().
- Disable SMP support for sun4m/sun4d. From the historic git
tree, it's unclear how well this ever worked, and very few machines
of this class ever existed
- Mark SMP for LEON as temporarily broken. As I see in the LEON
patch set, they have changes to enable compare-and-swap-atomic
instructions unconditionally, as all SMP Leons have those and
seem to require this support already for other things.
Arnd
next prev parent reply other threads:[~2020-12-15 11:27 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-07 9:14 [PATCH 1/2] futex: mark futex_detect_cmpxchg() as 'noinline' Arnd Bergmann
2019-03-07 9:14 ` [PATCH 2/2] ARM: futex: make futex_detect_cmpxchg more reliable Arnd Bergmann
2019-03-07 19:39 ` Nick Desaulniers
2019-03-07 23:48 ` Russell King - ARM Linux admin
2019-03-08 0:04 ` Nick Desaulniers
2019-03-08 9:54 ` Russell King - ARM Linux admin
2019-03-08 8:57 ` Ard Biesheuvel
2019-03-08 9:53 ` Russell King - ARM Linux admin
2019-03-08 10:08 ` Ard Biesheuvel
2019-03-08 10:16 ` Ard Biesheuvel
2019-03-08 10:56 ` Russell King - ARM Linux admin
2019-03-08 10:34 ` Russell King - ARM Linux admin
2019-03-08 10:45 ` Ard Biesheuvel
2019-03-08 10:58 ` Russell King - ARM Linux admin
2019-03-08 11:55 ` Ard Biesheuvel
2019-03-11 14:34 ` Arnd Bergmann
2019-03-11 14:36 ` Ard Biesheuvel
2019-03-11 16:29 ` Arnd Bergmann
2019-03-11 16:36 ` Ard Biesheuvel
2019-03-11 20:58 ` Arnd Bergmann
2019-03-08 11:55 ` Dave Martin
2019-03-07 17:19 ` [PATCH 1/2] futex: mark futex_detect_cmpxchg() as 'noinline' Joe Perches
2019-03-07 17:25 ` Russell King - ARM Linux admin
2019-03-07 17:42 ` Joe Perches
2019-03-07 18:07 ` Russell King - ARM Linux admin
2019-03-07 18:12 ` Nick Desaulniers
2019-03-07 18:21 ` Nathan Chancellor
2019-03-07 22:24 ` Arnd Bergmann
2020-12-12 12:26 ` Marco Elver
2020-12-12 20:01 ` Thomas Gleixner
2020-12-14 10:22 ` Marco Elver
2020-12-14 13:15 ` Arnd Bergmann
2020-12-15 6:09 ` Guo Ren
2020-12-15 11:26 ` Arnd Bergmann [this message]
2020-12-15 19:38 ` Sam Ravnborg
2020-12-15 23:24 ` Arnd Bergmann
2020-12-17 15:32 ` Andreas Larsson
2020-12-17 16:43 ` Arnd Bergmann
2020-12-18 11:08 ` Andreas Larsson
2020-12-17 20:03 ` Sam Ravnborg
2020-12-16 10:07 ` David Laight
2020-12-16 11:40 ` Peter Zijlstra
2020-12-20 15:44 ` Guo Ren
2020-12-20 17:49 ` Arnd Bergmann
2020-12-21 2:58 ` Guo Ren
2021-07-22 20:05 ` Nathan Chancellor
2021-10-25 13:52 ` Arnd Bergmann
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