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Date:   Thu, 29 Jul 2021 13:35:23 +0100
From:   Will Deacon <will@kernel.org>
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     Rui Wang <wangrui@loongson.cn>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Waiman Long <longman@redhat.com>,
        Boqun Feng <boqun.feng@gmail.com>, Guo Ren <guoren@kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Rui Wang <r@hev.cc>, Xuefeng Li <lixuefeng@loongson.cn>,
        Huacai Chen <chenhuacai@gmail.com>,
        Jiaxun Yang <jiaxun.yang@flygoat.com>,
        Huacai Chen <chenhuacai@loongson.cn>,
        kernel test robot <lkp@intel.com>
Subject: Re: [RFC PATCH v3] locking/atomic: Implement
 atomic{,64,_long}_{fetch_,}{andnot_or}{,_relaxed,_acquire,_release}()
Message-ID: <20210729123522.GB21766@willie-the-truck>
References: <20210729093003.146166-1-wangrui@loongson.cn>
 <20210729095551.GE21151@willie-the-truck>
 <CAK8P3a3ru0VSYLohoFOd=P=Fjb8BS=1qpMGSf4jdxF4oxmH-ag@mail.gmail.com>
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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@kernel.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