From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <mst@redhat.com>
Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28])
 by dpdk.org (Postfix) with ESMTP id 696218E95
 for <dev@dpdk.org>; Thu, 21 Jan 2016 20:03:32 +0100 (CET)
Received: from int-mx13.intmail.prod.int.phx2.redhat.com
 (int-mx13.intmail.prod.int.phx2.redhat.com [10.5.11.26])
 by mx1.redhat.com (Postfix) with ESMTPS id 9F0EC461D5;
 Thu, 21 Jan 2016 19:03:31 +0000 (UTC)
Received: from redhat.com (vpn1-6-206.ams2.redhat.com [10.36.6.206])
 by int-mx13.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with SMTP id
 u0LJ3SZn013385; Thu, 21 Jan 2016 14:03:28 -0500
Date: Thu, 21 Jan 2016 21:03:27 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
To: Cornelia Huck <cornelia.huck@de.ibm.com>
Message-ID: <20160121210230-mutt-send-email-mst@redhat.com>
References: <20160121145418-mutt-send-email-mst@redhat.com>
 <20160121163836.1091943d.cornelia.huck@de.ibm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20160121163836.1091943d.cornelia.huck@de.ibm.com>
X-Scanned-By: MIMEDefang 2.68 on 10.5.11.26
Cc: virtio-dev@lists.oasis-open.org, kvm@vger.kernel.org, dev@dpdk.org,
 linux-kernel@vger.kernel.org, qemu-devel@nongnu.org,
 virtio@lists.oasis-open.org, virtualization@lists.linux-foundation.org
Subject: Re: [dpdk-dev] virtio ring layout changes for optimal single-stream
	performance
X-BeenThere: dev@dpdk.org
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: patches and discussions about DPDK <dev.dpdk.org>
List-Unsubscribe: <http://dpdk.org/ml/options/dev>,
 <mailto:dev-request@dpdk.org?subject=unsubscribe>
List-Archive: <http://dpdk.org/ml/archives/dev/>
List-Post: <mailto:dev@dpdk.org>
List-Help: <mailto:dev-request@dpdk.org?subject=help>
List-Subscribe: <http://dpdk.org/ml/listinfo/dev>,
 <mailto:dev-request@dpdk.org?subject=subscribe>
X-List-Received-Date: Thu, 21 Jan 2016 19:03:32 -0000

On Thu, Jan 21, 2016 at 04:38:36PM +0100, Cornelia Huck wrote:
> On Thu, 21 Jan 2016 15:39:26 +0200
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > Hi all!
> > I have been experimenting with alternative virtio ring layouts,
> > in order to speed up single stream performance.
> > 
> > I have just posted a benchmark I wrote for the purpose, and a (partial)
> > alternative layout implementation.  This achieves 20-40% reduction in
> > virtio overhead in the (default) polling mode.
> > 
> > http://article.gmane.org/gmane.linux.kernel.virtualization/26889
> > 
> > The layout is trying to be as simple as possible, to reduce
> > the number of cache lines bouncing between CPUs.
> 
> Some kind of diagram or textual description would really help to review
> this.
> 
> > 
> > For benchmarking, the idea is to emulate virtio in user-space,
> > artificially adding overhead for e.g. signalling to match what happens
> > in case of a VM.
> 
> Hm... is this overhead comparable enough between different platform so
> that you can get a halfway realistic scenario?

On x86 is seems pretty stable.
It's a question of setting VMEXIT_CYCLES and VMENTRY_CYCLES correctly.

> What about things like
> endianness conversions?

I didn't bother with them yet.

> > 
> > I'd be very curious to get feedback on this, in particular, some people
> > discussed using vectored operations to format virtio ring - would it
> > conflict with this work?
> > 
> > You are all welcome to post enhancements or more layout alternatives as
> > patches.
> 
> Let me see if I can find time to experiment a bit.