From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 41kWrN5zHMzF3HJ for ; Mon, 6 Aug 2018 19:02:43 +1000 (AEST) Received: from pps.filterd (m0098421.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w768xUOf068550 for ; Mon, 6 Aug 2018 05:02:40 -0400 Received: from e06smtp07.uk.ibm.com (e06smtp07.uk.ibm.com [195.75.94.103]) by mx0a-001b2d01.pphosted.com with ESMTP id 2kphp0v7h4-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Mon, 06 Aug 2018 05:02:40 -0400 Received: from localhost by e06smtp07.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 6 Aug 2018 10:02:38 +0100 Subject: Re: [RFC 0/4] Virtio uses DMA API for all devices To: "Michael S. Tsirkin" , Benjamin Herrenschmidt References: <20180720035941.6844-1-khandual@linux.vnet.ibm.com> <20180802235332-mutt-send-email-mst@kernel.org> <20180803220812-mutt-send-email-mst@kernel.org> <01c74680c4b3aa25d9b4375a9ab5e10046b7c71b.camel@kernel.crashing.org> <20180805032355-mutt-send-email-mst@kernel.org> Cc: robh@kernel.org, srikar@linux.vnet.ibm.com, aik@ozlabs.ru, Jason Wang , linuxram@us.ibm.com, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, hch@infradead.org, paulus@samba.org, joe@perches.com, david@gibson.dropbear.id.au, linuxppc-dev@lists.ozlabs.org, elfring@users.sourceforge.net, haren@linux.vnet.ibm.com From: Anshuman Khandual Date: Mon, 6 Aug 2018 14:32:28 +0530 MIME-Version: 1.0 In-Reply-To: <20180805032355-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=windows-1252 Message-Id: <74a1e1b8-81e0-84db-6d0d-d8bd9caebb4a@linux.vnet.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 08/05/2018 05:54 AM, Michael S. Tsirkin wrote: > On Fri, Aug 03, 2018 at 08:21:26PM -0500, Benjamin Herrenschmidt wrote: >> On Fri, 2018-08-03 at 22:08 +0300, Michael S. Tsirkin wrote: >>>>>> Please go through these patches and review whether this approach broadly >>>>>> makes sense. I will appreciate suggestions, inputs, comments regarding >>>>>> the patches or the approach in general. Thank you. >>>>> >>>>> Jason did some work on profiling this. Unfortunately he reports >>>>> about 4% extra overhead from this switch on x86 with no vIOMMU. >>>> >>>> The test is rather simple, just run pktgen (pktgen_sample01_simple.sh) in >>>> guest and measure PPS on tap on host. >>>> >>>> Thanks >>> >>> Could you supply host configuration involved please? >> >> I wonder how much of that could be caused by Spectre mitigations >> blowing up indirect function calls... >> >> Cheers, >> Ben. > > I won't be surprised. If yes I suggested a way to mitigate the overhead. Did we get better results (lower regression due to indirect calls) with the suggested mitigation ? Just curious.