From: David Laight <david.laight.linux@gmail.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: linux-arm-kernel@lists.infradead.org, ada.coupriediaz@arm.com,
ardb@kernel.org, catalin.marinas@arm.com, hca@linux.ibm.com,
linux-kernel@vger.kernel.org, maz@kernel.org,
peterz@infradead.org, ruanjinjie@huawei.com,
vladimir.murzin@arm.com, will@kernel.org,
yang@os.amperecomputing.com
Subject: Re: [RFC PATCH 07/13] arm64: percpu: Implement preemptible read/write ops
Date: Tue, 28 Jul 2026 22:47:55 +0100 [thread overview]
Message-ID: <20260728224755.59cfd22d@pumpkin> (raw)
In-Reply-To: <20260728123859.2911495-8-mark.rutland@arm.com>
On Tue, 28 Jul 2026 13:38:53 +0100
Mark Rutland <mark.rutland@arm.com> wrote:
> Use the PCPU GPR infrastructure to implement preemptible this_cpu_read()
> and this_cpu_write().
...
> #define this_cpu_write_1(pcp, val) \
> - _pcp_protect(__percpu_write_8, pcp, (unsigned long)val)
> + _pcp_wrap(__percpu_write_8, pcp, (unsigned long)val)
Not new, but does that end up sign extending 'val' which is likely
to be more expensive than zero extending it?
Using '(val) + 0u + 0ul' might generate better code in some cases.
Just noticed it should be (unsigned long)(val) as well.
Otherwise this_cpu_write_n(pcp, -7 / 4) isn't going to DTRT.
David
> #define this_cpu_write_2(pcp, val) \
> - _pcp_protect(__percpu_write_16, pcp, (unsigned long)val)
> + _pcp_wrap(__percpu_write_16, pcp, (unsigned long)val)
> #define this_cpu_write_4(pcp, val) \
> - _pcp_protect(__percpu_write_32, pcp, (unsigned long)val)
> + _pcp_wrap(__percpu_write_32, pcp, (unsigned long)val)
> #define this_cpu_write_8(pcp, val) \
> - _pcp_protect(__percpu_write_64, pcp, (unsigned long)val)
> + _pcp_wrap(__percpu_write_64, pcp, (unsigned long)val)
>
> #define this_cpu_add_1(pcp, val) \
> _pcp_protect(__percpu_add_case_8, pcp, val)
next prev parent reply other threads:[~2026-07-28 21:47 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-28 12:38 [RFC PATCH 00/13] arm64: Preemptible this_cpu_*() operations Mark Rutland
2026-07-28 12:38 ` [RFC PATCH 01/13] arm64: preempt: Simplify and optimize __preempt_count_dec_and_test() Mark Rutland
2026-07-28 12:38 ` [RFC PATCH 02/13] arm64: preempt: Treat should_resched() as unlikely Mark Rutland
2026-07-28 12:38 ` [RFC PATCH 03/13] arm64: ptrace: Always inline pt_regs_[read,write}_reg() Mark Rutland
2026-07-28 12:38 ` [RFC PATCH 04/13] arm64: percpu: Factor out percpu offset asm Mark Rutland
2026-07-28 12:38 ` [RFC PATCH 05/13] arm64: gpr-num: Add wxN aliases for wN registers Mark Rutland
2026-07-28 12:38 ` [RFC PATCH 06/13] arm64: percpu: Add infrastructure for preemptible this_cpu_*() ops Mark Rutland
2026-07-28 14:19 ` Peter Zijlstra
2026-07-28 14:30 ` Peter Zijlstra
2026-07-28 16:03 ` Mark Rutland
2026-07-28 16:49 ` Peter Zijlstra
2026-07-28 15:53 ` Mark Rutland
2026-07-28 16:46 ` Peter Zijlstra
2026-07-28 16:49 ` Peter Zijlstra
2026-07-28 16:51 ` Heiko Carstens
2026-07-28 12:38 ` [RFC PATCH 07/13] arm64: percpu: Implement preemptible read/write ops Mark Rutland
2026-07-28 21:47 ` David Laight [this message]
2026-07-28 22:05 ` David Laight
2026-07-28 12:38 ` [RFC PATCH 08/13] arm64: percpu: Implement preemptible void RMW ops Mark Rutland
2026-07-28 12:38 ` [RFC PATCH 09/13] arm64: percpu: Implement preemptible return " Mark Rutland
2026-07-28 12:38 ` [RFC PATCH 10/13] arm64: percpu: Implement preemptible XCHG ops Mark Rutland
2026-07-28 12:38 ` [RFC PATCH 11/13] arm64: percpu: Implement preemptible CMPXCHG ops Mark Rutland
2026-07-28 12:38 ` [RFC PATCH 12/13] arm64: percpu: Implement preemptible CMPXCHG128 ops Mark Rutland
2026-07-28 12:38 ` [RFC PATCH 13/13] arm64: percpu: Remove _pcp_protect*() wrappers Mark Rutland
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