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Date: Wed, 16 Dec 2020 12:40:30 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Arnd Bergmann <arnd@...nel.org> Cc: Guo Ren <guoren@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Marco Elver <elver@...gle.com>, Arnd Bergmann <arnd@...db.de>, Russell King <linux@...linux.org.uk>, Ingo Molnar <mingo@...hat.com>, Darren Hart <dvhart@...radead.org>, Nick Desaulniers <ndesaulniers@...gle.com>, Davidlohr Bueso <dave@...olabs.net>, Elena Reshetova <elena.reshetova@...el.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, linux-csky@...r.kernel.org, sparclinux <sparclinux@...r.kernel.org>, "David S. Miller" <davem@...emloft.net> Subject: Re: [PATCH 1/2] futex: mark futex_detect_cmpxchg() as 'noinline' On Tue, Dec 15, 2020 at 12:26:10PM +0100, Arnd Bergmann wrote: > On Tue, Dec 15, 2020 at 7:09 AM Guo Ren <guoren@...nel.org> wrote: > > On Mon, Dec 14, 2020 at 9:15 PM Arnd Bergmann <arnd@...nel.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 Hooray!! what about PA-RISC ? Can we burn that too?
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