From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [net-next PATCH v2 0/5] XDP adjust head support for virtio Date: Wed, 8 Feb 2017 18:50:56 +0200 Message-ID: <20170208184817-mutt-send-email-mst@kernel.org> References: <20170203031251.23054.25387.stgit@john-Precision-Tower-5810> <20170207053455-mutt-send-email-mst@kernel.org> <589B49B1.4070304@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kubakici@wp.pl, jasowang@redhat.com, ast@fb.com, john.r.fastabend@intel.com, netdev@vger.kernel.org To: John Fastabend Return-path: Received: from mx1.redhat.com ([209.132.183.28]:59532 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752529AbdBHQ6a (ORCPT ); Wed, 8 Feb 2017 11:58:30 -0500 Content-Disposition: inline In-Reply-To: <589B49B1.4070304@gmail.com> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, Feb 08, 2017 at 08:39:13AM -0800, John Fastabend wrote: > [...] > > > However, I came up with a new idea for the future and I'd like to show > > where I'm going. The idea is that we don't use s/g buffers on RX, so we > > have a pointer per descriptor untapped. So we can allow users to stick > > their own pointer in there, if they promise not to use s/g on this vq. > > With a full extra pointer to play with, we can go wild. > > I looked at this quickly it seems like it would work and allow us to avoid > the reset. However, it seems like a lot of churn to avoid a single reset. > I don't see the reset itself as being that bad of an operation. I agree the > reset is not ideal though. > > Are there any other use cases for this other than XDP? Well in fact this would allow reducing MERGEABLE_BUFFER_ALIGN to L1_CACHE_BYTES so we save space per packet for regular networking. The idea to use build_skb would also benefit accordingly. I guess ndo_set_rx_headroom could benefit if we were to implement that. > > > > Take a look but it doesn't even build yet. > > Need to roll it out to all devices etc. > > > > ---> > > > > [...]