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Thu, 18 Mar 2021 18:45:13 +0000 From: "Ankur Arora" To: devel@edk2.groups.io Cc: Ankur Arora , Liming Gao , Michael D Kinney , Laszlo Ersek Subject: [edk2-devel] [PATCH v2] MdePkg: use CpuPause() in CpuDeadLoop() Date: Thu, 18 Mar 2021 11:45:04 -0700 Message-Id: <20210318184504.2745112-1-ankur.a.arora@oracle.com> X-Originating-IP: [148.87.23.7] X-ClientProxiedBy: MWHPR1701CA0016.namprd17.prod.outlook.com (2603:10b6:301:14::26) To SJ0PR10MB4605.namprd10.prod.outlook.com (2603:10b6:a03:2d9::24) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 X-Received: from prion.us.oracle.com (148.87.23.7) by MWHPR1701CA0016.namprd17.prod.outlook.com (2603:10b6:301:14::26) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3955.18 via Frontend Transport; Thu, 18 Mar 2021 18:45:12 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 270b359d-75ba-4945-34c7-08d8ea3df6ea X-MS-TrafficTypeDiagnostic: BYAPR10MB3557: X-MS-Exchange-Transport-Forked: True X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:7691; 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contact devel+owner@edk2.groups.io Reply-To: devel@edk2.groups.io,ankur.a.arora@oracle.com X-Gm-Message-State: he1hYlfcpdMHfQQ5gwttDXXyx1787277AA= Content-Transfer-Encoding: quoted-printable DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=groups.io; q=dns/txt; s=20140610; t=1616093147; bh=dbAAV7o5hAfx7YZF5Uqpq17r6RxgCx76sHA0tlhffVc=; h=Cc:Content-Type:Date:From:Reply-To:Subject:To; b=W9pXGkofaoCQ5BfkBOzcgRf6MRJYEBo6mP7YyeTWYJhW6ve2CsXRKbYqrAqNthkYv/y R3t9v+Dt9it+z+Hemi/bS+/lIzY3olHYCm1/unWYjtFHsJ9MZ0SbXcGrB9iQ6nYaQpx3b 5VLIqBXJEnyi5ohElY+KvGTl1eqF75ZKJr8= X-ZohoMail-DKIM: pass (identity @groups.io) Content-Type: text/plain; charset="utf-8" CpuPause() might allow the CPU to go into a lower power state state while we spin. On X86, CpuPause() executes a PAUSE instruction which the Intel and AMD specs describe as follows: Intel: "PAUSE: An additional function of the PAUSE instruction is to reduce the power consumed by a processor while executing a spin loop. A processor can execute a spin-wait loop extremely quickly, causing the processor to consume a lot of power while it waits for the resource it is spinning on to become available. Inserting a pause instruction in a spin-wait loop greatly reduces the processor=E2=80=99s power consumption." AMD: "PAUSE: Improves the performance of spin loops, by providing a hint to the processor that the current code is in a spin loop. The processor may use this to optimize power consumption while in the spin loop. Architecturally, this instruction behaves like a NOP instruction." On RISC-V and ARM64, CpuPause() executes a NOP, which is no worse than the tight loop we have. Cc: Liming Gao Signed-off-by: Ankur Arora Reviewed-by: Michael D Kinney Reviewed-by: Laszlo Ersek --- MdePkg/Library/BaseLib/CpuDeadLoop.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/MdePkg/Library/BaseLib/CpuDeadLoop.c b/MdePkg/Library/BaseLib/= CpuDeadLoop.c index 9e110cacbc96..3cd304351a65 100644 --- a/MdePkg/Library/BaseLib/CpuDeadLoop.c +++ b/MdePkg/Library/BaseLib/CpuDeadLoop.c @@ -28,5 +28,7 @@ CpuDeadLoop ( { volatile UINTN Index; =20 - for (Index =3D 0; Index =3D=3D 0;); + for (Index =3D 0; Index =3D=3D 0;) { + CpuPause(); + } } --=20 2.9.3 -=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#73018): https://edk2.groups.io/g/devel/message/73018 Mute This Topic: https://groups.io/mt/81437102/1787277 Group Owner: devel+owner@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [importer@patchew.org] -=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-=3D-