From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 41jhNz31rBzF3Hb for ; Sun, 5 Aug 2018 10:24:35 +1000 (AEST) Date: Sun, 5 Aug 2018 03:24:28 +0300 From: "Michael S. Tsirkin" To: Benjamin Herrenschmidt Cc: Jason Wang , Anshuman Khandual , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, aik@ozlabs.ru, robh@kernel.org, joe@perches.com, elfring@users.sourceforge.net, david@gibson.dropbear.id.au, mpe@ellerman.id.au, hch@infradead.org, linuxram@us.ibm.com, haren@linux.vnet.ibm.com, paulus@samba.org, srikar@linux.vnet.ibm.com Subject: Re: [RFC 0/4] Virtio uses DMA API for all devices Message-ID: <20180805032355-mutt-send-email-mst@kernel.org> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <01c74680c4b3aa25d9b4375a9ab5e10046b7c71b.camel@kernel.crashing.org> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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. -- MSR