linux-kernel - Re: [RFC PATCH v3] locking/atomic: Implement atomic{,64,_long}_{fetch_,}{andnot_or}{,_relaxed,_acquire,

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Message-ID: <CAHirt9iYhmQPjMNn_RxBib8fumR0RhjVoBN1ggGm-9MSMHu4Rw@mail.gmail.com>
Date:   Fri, 30 Jul 2021 10:50:53 +0800
From:   hev <r@....cc>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Will Deacon <will@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Rui Wang <wangrui@...ngson.cn>, Ingo Molnar <mingo@...hat.com>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>, Guo Ren <guoren@...nel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Xuefeng Li <lixuefeng@...ngson.cn>,
        Huacai Chen <chenhuacai@...il.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Huacai Chen <chenhuacai@...ngson.cn>,
        kernel test robot <lkp@...el.com>
Subject: Re: [RFC PATCH v3] locking/atomic: Implement atomic{,64,_long}_{fetch_,}{andnot_or}{,_relaxed,_acquire,_release}()

Hi,

On Thu, Jul 29, 2021 at 8:35 PM Will Deacon <will@...nel.org> wrote:
>
> On Thu, Jul 29, 2021 at 01:43:41PM +0200, Arnd Bergmann wrote:
> > On Thu, Jul 29, 2021 at 11:56 AM Will Deacon <will@...nel.org> wrote:
> > > On Thu, Jul 29, 2021 at 05:30:03PM +0800, Rui Wang wrote:
> > > > This patch introduce a new atomic primitive andnot_or:
> > >
> > > Please see my other comments on the other patches you posted:
> > >
> > > https://lore.kernel.org/r/20210729093923.GD21151@willie-the-truck
> > >
> > > Overall, I'm not thrilled to bits by extending the atomics API with
> > > operations that cannot be implemented efficiently on any (?) architectures
> > > and are only used by the qspinlock slowpath on machines with more than 16K
> > > CPUs.
> >
> > Wouldn't this also help improve set_mask_bits()? That one at least has
> > a handful of users in the kernel.
>
> For pure LL/SC architectures, yes, but I don't think it helps anybody else.
>
> Afaict, an architecture can already override set_mask_bits, so why do we
> need to add this primitive to the atomic API?
>
> Will

So what's next?

Now the set_mask_bits return oldval, return newval before 5.0. :-D
commit 1db604f676b("include/linux/bitops.h: set_mask_bits() to return
old value")

Regards,
Rui