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=-5.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS, USER_AGENT_MUTT autolearn=ham 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 E689BC43381 for ; Fri, 22 Feb 2019 09:46:57 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (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 8B61F2081B for ; Fri, 22 Feb 2019 09:46:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=ozlabs.org header.i=@ozlabs.org header.b="Fy/MOjvB" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8B61F2081B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ozlabs.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 445RM346JxzDqTy for ; Fri, 22 Feb 2019 20:46:55 +1100 (AEDT) Received: from ozlabs.org (bilbo.ozlabs.org [203.11.71.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 445RGv0rP3zDqTV for ; Fri, 22 Feb 2019 20:43:19 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=ozlabs.org Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; secure) header.d=ozlabs.org header.i=@ozlabs.org header.b="Fy/MOjvB"; dkim-atps=neutral Received: by ozlabs.org (Postfix, from userid 1003) id 445RGt5Lwnz9sB8; Fri, 22 Feb 2019 20:43:18 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ozlabs.org; s=201707; t=1550828598; bh=kkFZR+1x5t2SxE1DFisnUOo0pFDJKpb0vUMXGH8St04=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Fy/MOjvBzMssZMdqsA2wZrKSuozdKv3Ut4mlPSeW7WeuKej+H9VEepNax4ZvAzkD/ 17nzEEQhi2suTxELUfAPFgxUyWctshGXSi70PaTsPl+1bSpX0hg5srVRTnSpcn1miU TJjVTfqcVshK13tj1C5EMfhs/vVAlnh+HiZfEG7BYlC1igu6P3+sf8BkorTW+njJw+ 9oMPri+lxS68/Zf6w0Vg611cqBfuNkEkNmVOAAhEF4G2k+ysaTdgxyc6UFKok4wfnn sRJWBqUdI39DVIHLqoMi4MJGLAimU8kKmmB8psbEuE20WUWnxbmL3UMGP0egflniZp cASWobX+em6/A== Date: Fri, 22 Feb 2019 20:39:02 +1100 From: Paul Mackerras To: Suraj Jitindar Singh Subject: Re: [PATCH] KVM: PPC: Book3S HV: Optimise mmio emulation for devices on FAST_MMIO_BUS Message-ID: <20190222093902.GB6006@blackberry> References: <20190207045650.18322-1-sjitindarsingh@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190207045650.18322-1-sjitindarsingh@gmail.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Thu, Feb 07, 2019 at 03:56:50PM +1100, Suraj Jitindar Singh wrote: > Devices on the KVM_FAST_MMIO_BUS by definition have length zero and are > thus used for notification purposes rather than data transfer. For > example eventfd for virtio devices. > > This means that when emulating mmio instructions which target devices on > this bus we can immediately handle them and return without needing to load > the instruction from guest memory. > > For now we restrict this to stores as this is the only use case at > present. > > For a normal guest the effect is negligible, however for a nested guest > we save on the order of 5us per access. > > Signed-off-by: Suraj Jitindar Singh Thanks, applied to my kvm-ppc-next tree. Paul.