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From: Christoph Lameter <cl@linux.com>
To: Mihai Carabas <mihai.carabas@oracle.com>
Cc: linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org,
	linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
	catalin.marinas@arm.com, will@kernel.org, tglx@linutronix.de,
	mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com,
	pbonzini@redhat.com, wanpengli@tencent.com, vkuznets@redhat.com,
	rafael@kernel.org, daniel.lezcano@linaro.org,
	akpm@linux-foundation.org, pmladek@suse.com,
	peterz@infradead.org, dianders@chromium.org, npiggin@gmail.com,
	rick.p.edgecombe@intel.com, joao.m.martins@oracle.com,
	juerg.haefliger@canonical.com, mic@digikod.net, arnd@arndb.de,
	ankur.a.arora@oracle.com
Subject: Re: [PATCH 7/7] cpuidle/poll_state: replace cpu_relax with smp_cond_load_relaxed
Date: Wed, 22 Nov 2023 12:51:19 -0800 (PST)	[thread overview]
Message-ID: <6bd5fd43-552d-b020-1338-d89279f7a517@linux.com> (raw)
In-Reply-To: <1700488898-12431-8-git-send-email-mihai.carabas@oracle.com>


On Mon, 20 Nov 2023, Mihai Carabas wrote:

> cpu_relax on ARM64 does a simple "yield". Thus we replace it with
> smp_cond_load_relaxed which basically does a "wfe".

Well it clears events first (which requires the first WFE) and then does a 
WFE waiting for any events if no events were pending.

WFE does not cause a VMEXIT? Or does the inner loop of 
smp_cond_load_relaxed now do 2x VMEXITS?

KVM ARM64 code seems to indicate that WFE causes a VMEXIT. See 
kvm_handle_wfx().

WARNING: multiple messages have this Message-ID (diff)
From: Christoph Lameter <cl@linux.com>
To: Mihai Carabas <mihai.carabas@oracle.com>
Cc: linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org,
	 linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
	 catalin.marinas@arm.com, will@kernel.org, tglx@linutronix.de,
	 mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com,
	 pbonzini@redhat.com, wanpengli@tencent.com, vkuznets@redhat.com,
	 rafael@kernel.org, daniel.lezcano@linaro.org,
	akpm@linux-foundation.org,  pmladek@suse.com,
	peterz@infradead.org, dianders@chromium.org,  npiggin@gmail.com,
	rick.p.edgecombe@intel.com, joao.m.martins@oracle.com,
	 juerg.haefliger@canonical.com, mic@digikod.net, arnd@arndb.de,
	 ankur.a.arora@oracle.com
Subject: Re: [PATCH 7/7] cpuidle/poll_state: replace cpu_relax with smp_cond_load_relaxed
Date: Wed, 22 Nov 2023 12:51:19 -0800 (PST)	[thread overview]
Message-ID: <6bd5fd43-552d-b020-1338-d89279f7a517@linux.com> (raw)
In-Reply-To: <1700488898-12431-8-git-send-email-mihai.carabas@oracle.com>


On Mon, 20 Nov 2023, Mihai Carabas wrote:

> cpu_relax on ARM64 does a simple "yield". Thus we replace it with
> smp_cond_load_relaxed which basically does a "wfe".

Well it clears events first (which requires the first WFE) and then does a 
WFE waiting for any events if no events were pending.

WFE does not cause a VMEXIT? Or does the inner loop of 
smp_cond_load_relaxed now do 2x VMEXITS?

KVM ARM64 code seems to indicate that WFE causes a VMEXIT. See 
kvm_handle_wfx().

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2023-11-22 20:51 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-11-20 14:01 [PATCH v2] Enable haltpoll for arm64 Mihai Carabas
2023-11-20 14:01 ` Mihai Carabas
2023-11-20 14:01 ` [PATCH 1/7] x86: Move ARCH_HAS_CPU_RELAX to arch Mihai Carabas
2023-11-20 14:01   ` Mihai Carabas
2023-11-27 14:44   ` Petr Mladek
2023-11-27 14:44     ` Petr Mladek
2023-11-28 14:09     ` Mihai Carabas
2023-11-28 14:09       ` Mihai Carabas
2023-11-20 14:01 ` [PATCH 2/7] x86/kvm: Move haltpoll_want() to be arch defined Mihai Carabas
2023-11-20 14:01   ` Mihai Carabas
2023-11-29 20:55   ` Rafael J. Wysocki
2023-11-29 20:55     ` Rafael J. Wysocki
2023-11-20 14:01 ` [PATCH 3/7] governors/haltpoll: Drop kvm_para_available() check Mihai Carabas
2023-11-20 14:01   ` Mihai Carabas
2023-11-20 14:01 ` [PATCH 4/7] arm64: Select ARCH_HAS_CPU_RELAX Mihai Carabas
2023-11-20 14:01   ` Mihai Carabas
2023-11-20 14:01 ` [PATCH 5/7] arm64: Define TIF_POLLING_NRFLAG Mihai Carabas
2023-11-20 14:01   ` Mihai Carabas
2023-11-20 14:01 ` [PATCH 6/7] cpuidle-haltpoll: ARM64 support Mihai Carabas
2023-11-20 14:01   ` Mihai Carabas
2023-11-20 14:01 ` [PATCH 7/7] cpuidle/poll_state: replace cpu_relax with smp_cond_load_relaxed Mihai Carabas
2023-11-20 14:01   ` Mihai Carabas
2023-11-22 20:51   ` Christoph Lameter [this message]
2023-11-22 20:51     ` Christoph Lameter
2023-11-22 21:33     ` Mihai Carabas
2023-11-22 21:33       ` Mihai Carabas
2023-11-27 20:17       ` Christoph Lameter (Ampere)
2023-11-27 20:17         ` Christoph Lameter (Ampere)
2023-12-01  6:59         ` Ankur Arora
2023-12-01  6:59           ` Ankur Arora
2023-12-11 11:46   ` Will Deacon
2023-12-11 11:46     ` Will Deacon
2024-01-28 21:22     ` Mihai Carabas
2024-01-28 21:22       ` Mihai Carabas
2024-01-29 18:15       ` Will Deacon
2024-01-29 18:15         ` Will Deacon
2024-02-05 12:28         ` Mihai Carabas
2024-02-05 12:28           ` Mihai Carabas
2024-02-05 19:33           ` Ankur Arora
2024-02-05 19:33             ` Ankur Arora
2024-01-17 21:19 ` [PATCH v2] Enable haltpoll for arm64 Christoph Lameter (Ampere)
2024-01-17 21:19   ` Christoph Lameter (Ampere)
2024-01-25 14:39 ` Mihai Carabas
2024-01-25 14:39   ` Mihai Carabas
2024-01-25 15:16   ` Rafael J. Wysocki
2024-01-25 15:16     ` Rafael J. Wysocki

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