From: Catalin Marinas <catalin.marinas@arm.com>
To: Haris Okanovic <harisokn@amazon.com>
Cc: ankur.a.arora@oracle.com, linux-pm@vger.kernel.org,
kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, will@kernel.org,
tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com,
pbonzini@redhat.com, wanpengli@tencent.com, vkuznets@redhat.com,
rafael@kernel.org, daniel.lezcano@linaro.org,
peterz@infradead.org, arnd@arndb.de, lenb@kernel.org,
mark.rutland@arm.com, mtosatti@redhat.com, sudeep.holla@arm.com,
cl@gentwo.org, misono.tomohiro@fujitsu.com, maobibo@loongson.cn,
joao.m.martins@oracle.com, boris.ostrovsky@oracle.com,
konrad.wilk@oracle.com
Subject: Re: [PATCH 3/5] arm64: refactor delay() to enable polling for value
Date: Wed, 6 Nov 2024 09:18:04 +0000 [thread overview]
Message-ID: <Zys0TAHZzqbGst93@arm.com> (raw)
In-Reply-To: <20241105183041.1531976-4-harisokn@amazon.com>
On Tue, Nov 05, 2024 at 12:30:39PM -0600, Haris Okanovic wrote:
> + do {
> + cur = __READ_ONCE_EX(*addr);
> + if ((cur & mask) == val) {
> + break;
> + }
> wfet(end);
Constructs like this need to be entirely in assembly. The compiler may
spill 'cur' onto the stack and the write could clear the exclusive
monitor which makes the wfet return immediately. That's highly CPU
implementation specific but it's the reason we have functions like
__cmpwait() in assembly (or whatever else deals with exclusives). IOW,
we can't have other memory accesses between the LDXR and whatever is
consuming the exclusive monitor armed state (typically STXR but WFE/WFET
can be another).
--
Catalin
next prev parent reply other threads:[~2024-11-06 9:55 UTC|newest]
Thread overview: 74+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-09-25 23:24 [PATCH v8 00/11] Enable haltpoll on arm64 Ankur Arora
2024-09-25 23:24 ` [PATCH v8 01/11] cpuidle/poll_state: poll via smp_cond_load_relaxed() Ankur Arora
2024-10-15 12:04 ` Catalin Marinas
2024-10-15 16:42 ` Christoph Lameter (Ampere)
2024-10-15 16:50 ` Catalin Marinas
2024-10-15 17:17 ` Christoph Lameter (Ampere)
2024-10-15 17:40 ` Catalin Marinas
2024-10-15 21:53 ` Ankur Arora
2024-10-15 22:28 ` Christoph Lameter (Ampere)
2024-10-16 7:06 ` Ankur Arora
2024-10-17 16:54 ` Christoph Lameter (Ampere)
2024-10-17 18:36 ` Ankur Arora
2024-10-15 22:40 ` Christoph Lameter (Ampere)
2024-10-16 9:54 ` Catalin Marinas
2024-10-17 16:56 ` Christoph Lameter (Ampere)
2024-10-17 18:15 ` Catalin Marinas
2024-10-17 19:34 ` Ankur Arora
2024-10-15 21:32 ` Ankur Arora
2024-10-16 6:20 ` maobibo
2024-10-16 10:06 ` Catalin Marinas
2024-10-16 15:13 ` Okanovic, Haris
2024-10-16 17:04 ` Ankur Arora
2024-10-16 18:04 ` Okanovic, Haris
2024-10-17 14:01 ` Catalin Marinas
2024-10-17 22:47 ` Ankur Arora
2024-10-18 11:05 ` Catalin Marinas
2024-10-18 19:00 ` Ankur Arora
2024-10-21 12:02 ` Catalin Marinas
2024-09-25 23:24 ` [PATCH v8 02/11] cpuidle: rename ARCH_HAS_CPU_RELAX to ARCH_HAS_OPTIMIZED_POLL Ankur Arora
2024-09-25 23:24 ` [PATCH v8 03/11] Kconfig: move ARCH_HAS_OPTIMIZED_POLL to arch/Kconfig Ankur Arora
2024-09-25 23:24 ` [PATCH v8 04/11] cpuidle-haltpoll: define arch_haltpoll_want() Ankur Arora
2024-09-25 23:24 ` [PATCH v8 05/11] governors/haltpoll: drop kvm_para_available() check Ankur Arora
2024-09-25 23:24 ` [PATCH v8 06/11] cpuidle-haltpoll: condition on ARCH_CPUIDLE_HALTPOLL Ankur Arora
2024-09-25 23:24 ` [PATCH v8 07/11] arm64: define TIF_POLLING_NRFLAG Ankur Arora
2024-09-25 23:24 ` [PATCH v8 08/11] arm64: idle: export arch_cpu_idle Ankur Arora
2024-09-25 23:24 ` [PATCH v8 09/11] arm64: select ARCH_HAS_OPTIMIZED_POLL Ankur Arora
2024-09-25 23:24 ` [PATCH v8 10/11] cpuidle/poll_state: limit POLL_IDLE_RELAX_COUNT on arm64 Ankur Arora
2024-09-25 23:24 ` [PATCH v8 11/11] arm64: support cpuidle-haltpoll Ankur Arora
2024-10-02 22:42 ` Okanovic, Haris
2024-10-03 3:29 ` Ankur Arora
2024-10-16 15:13 ` Okanovic, Haris
2024-10-09 2:37 ` [PATCH v8 00/11] Enable haltpoll on arm64 zhenglifeng (A)
2024-10-15 1:53 ` Ankur Arora
2024-10-14 22:54 ` Christoph Lameter (Ampere)
2024-10-15 12:36 ` Marc Zyngier
2024-10-16 21:55 ` Ankur Arora
2024-10-17 8:19 ` Marc Zyngier
2024-10-17 18:35 ` Ankur Arora
2024-10-22 22:01 ` Ankur Arora
2024-11-05 18:30 ` Haris Okanovic
2024-11-05 18:30 ` [PATCH 1/5] asm-generic: add smp_vcond_load_relaxed() Haris Okanovic
2024-11-05 19:36 ` Christoph Lameter (Ampere)
2024-11-06 17:06 ` Okanovic, Haris
2024-11-06 11:08 ` Catalin Marinas
2024-11-06 18:13 ` Okanovic, Haris
2024-11-06 19:55 ` Catalin Marinas
2024-11-06 20:31 ` Okanovic, Haris
2024-11-06 11:39 ` Will Deacon
2024-11-06 17:18 ` Okanovic, Haris
2024-11-05 18:30 ` [PATCH 2/5] arm64: add __READ_ONCE_EX() Haris Okanovic
2024-11-05 19:39 ` Christoph Lameter (Ampere)
2024-11-06 17:37 ` Okanovic, Haris
2024-11-06 11:43 ` Will Deacon
2024-11-06 17:09 ` Okanovic, Haris
2024-11-09 9:49 ` David Laight
2024-11-05 18:30 ` [PATCH 3/5] arm64: refactor delay() to enable polling for value Haris Okanovic
2024-11-05 19:42 ` Christoph Lameter (Ampere)
2024-11-06 17:42 ` Okanovic, Haris
2024-11-06 9:18 ` Catalin Marinas [this message]
2024-11-06 17:38 ` Okanovic, Haris
2024-11-05 18:30 ` [PATCH 4/5] arm64: add smp_vcond_load_relaxed() Haris Okanovic
2024-11-05 18:30 ` [PATCH 5/5] cpuidle: implement poll_idle() using smp_vcond_load_relaxed() Haris Okanovic
2024-11-05 19:45 ` Christoph Lameter (Ampere)
2024-11-05 18:49 ` [PATCH v8 00/11] Enable haltpoll on arm64 Ankur Arora
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