From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D7400C2D0CF for ; Tue, 24 Dec 2019 13:46:29 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A709720730 for ; Tue, 24 Dec 2019 13:46:29 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="VerE/IMO" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A709720730 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender:Content-Type: Content-Transfer-Encoding:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:Message-ID:References:In-Reply-To:From:Date: MIME-Version:Subject:To:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=TParvIfFxc40ON4KPJw4bysXadKVEYTzdvpqqeYETw4=; b=VerE/IMOh2VZM6o5BAYrBY7Dw hYPueTtFYRZZP8QRa1LvlYASovX71lT0sRNeG4mtnff2uL03HDf2qoeVhNOaBFn4jwmsq3/ZRRuj2 hn/J5n1V19KPYaVjPVDXwioZfFWPJTW6nI6VQxFaN/k+BX8qdRY+ah3QKgul1rSg9ro96Qhr/huif jQHs+/7djVviqboyIaqcba2TE/Q6k6Llc26Nkt2ZRksCMpGna1W6T4VwnMmw76lzEs2lY+kle6x/V AUSwDzqT8D6/lMIAKzRgcKXDcnA0GyJsL309vwddCO2fkLuI9/q0SCAc+kHwwYovtfUfc9ZE8aKH4 Lqi0yhoTA==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1ijkVx-0002Bz-1s; Tue, 24 Dec 2019 13:46:21 +0000 Received: from inca-roads.misterjones.org ([213.251.177.50]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1ijkVu-0002B7-2i for linux-arm-kernel@lists.infradead.org; Tue, 24 Dec 2019 13:46:19 +0000 Received: from www-data by cheepnis.misterjones.org with local (Exim 4.80) (envelope-from ) id 1ijkVo-0003p4-RU; Tue, 24 Dec 2019 14:46:12 +0100 To: Andrew Murray Subject: Re: [PATCH v2 14/18] KVM: arm64: spe: Provide guest virtual interrupts for SPE X-PHP-Originating-Script: 0:main.inc MIME-Version: 1.0 Date: Tue, 24 Dec 2019 13:46:12 +0000 From: Marc Zyngier In-Reply-To: <20191224133647.GO42593@e119886-lin.cambridge.arm.com> References: <20191220143025.33853-1-andrew.murray@arm.com> <20191220143025.33853-15-andrew.murray@arm.com> <867e2oimw9.wl-maz@kernel.org> <20191224115031.GG42593@e119886-lin.cambridge.arm.com> <1f3fbff6c9db0f14c92a6e3fb800fa0f@www.loen.fr> <20191224130853.GN42593@e119886-lin.cambridge.arm.com> <20191224133647.GO42593@e119886-lin.cambridge.arm.com> Message-ID: X-Sender: maz@kernel.org User-Agent: Roundcube Webmail/0.7.2 X-SA-Exim-Connect-IP: X-SA-Exim-Rcpt-To: andrew.murray@arm.com, marc.zyngier@arm.com, catalin.marinas@arm.com, will.deacon@arm.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, sudeep.holla@arm.com, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on cheepnis.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191224_054618_267098_B4F5EE9D X-CRM114-Status: GOOD ( 11.40 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kvm@vger.kernel.org, Marc Zyngier , Catalin Marinas , Will Deacon , linux-kernel@vger.kernel.org, Sudeep Holla , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2019-12-24 13:36, Andrew Murray wrote: > On Tue, Dec 24, 2019 at 01:22:46PM +0000, Marc Zyngier wrote: >> On 2019-12-24 13:08, Andrew Murray wrote: [...] >> > This does feel like the pragmatic approach - a larger black hole >> in >> > exchange >> > for performance. I imagine the blackhole would be naturally >> reduced on >> > machines with high workloads. >> >> Why? I don't see the relation between how busy the vcpu is and the >> size >> of the blackhole. It is strictly a function of the frequency of >> exits. > > Indeed, my assumption being that the busier a system is the more > interrupts, thus leading to more exits and so an increased frequency > of > SPE interrupt evaluation and thus smaller black hole. On a GICv4-enabled system, this isn't true anymore. My bet is that people won't use SPE to optimize IO-oriented workloads, but more CPU intensive workloads (that don't necessarily exit at all). But never mind. Let's start with this approach, as it is simple and easy to verify. If the black hole aspect becomes problematic, we know how to reduce it (at the expense of entry/exit performance). M. -- Jazz is not dead. It just smells funny... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel