Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752586AbbBYNYj (ORCPT ); Wed, 25 Feb 2015 08:24:39 -0500 Received: from foss.arm.com ([217.140.101.70]:37485 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751852AbbBYNYi (ORCPT ); Wed, 25 Feb 2015 08:24:38 -0500 Date: Wed, 25 Feb 2015 13:24:38 +0000 From: Will Deacon To: Peter Crosthwaite Cc: "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Catalin Marinas , "michals@xilinx.com" Subject: Re: [RFC PATCH] arm64: Implement cpu_relax as yield Message-ID: <20150225132437.GD12377@arm.com> References: <1424819257-22664-1-git-send-email-peter.crosthwaite@xilinx.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1424819257-22664-1-git-send-email-peter.crosthwaite@xilinx.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 840 Lines: 18 On Tue, Feb 24, 2015 at 11:07:37PM +0000, Peter Crosthwaite wrote: > ARM64 has the yield nop hint which has the intended semantics of > cpu_relax. Implement. > > The immediate application is ARM CPU emulators. An emulator can take > advantage of the yield hint to de-prioritise an emulated CPU in favor > of other emulation tasks. QEMU A64 SMP emulation has yield awareness, > and sees a significant boot time performance increase with this change. Could you elaborate on the QEMU SMP boot case please? Usually SMP pens for booting make use of wfe/sev to minimise the spinning overhead. Will -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/