From mboxrd@z Thu Jan 1 00:00:00 1970 From: Shirley Ma Subject: Re: [PATCH V5 2/6 net-next] netdevice.h: Add zero-copy flag in netdevice Date: Wed, 25 May 2011 15:49:40 -0700 Message-ID: <1306363780.26270.44.camel@localhost.localdomain> References: <20110518111734.GO7589@redhat.com> <1305729507.32080.6.camel@localhost.localdomain> <20110518154746.GA21378@redhat.com> <1305734857.32080.53.camel@localhost.localdomain> <20110518163633.GB22001@redhat.com> <1305737140.32080.59.camel@localhost.localdomain> <20110518165138.GD22001@redhat.com> <1305738028.32080.66.camel@localhost.localdomain> <1305834169.32080.81.camel@localhost.localdomain> <20110519234154.GA13784@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: =?UTF-8?Q?Micha=C5=82_Miros=C5=82aw?= , Ben Hutchings , David Miller , Eric Dumazet , Avi Kivity , Arnd Bergmann , netdev@vger.kernel.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org To: "Michael S. Tsirkin" Return-path: In-Reply-To: <20110519234154.GA13784@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Fri, 2011-05-20 at 02:41 +0300, Michael S. Tsirkin wrote: > So the requirements are > - data must be released in a timely fashion (e.g. unlike virtio-net > tun or bridge) The current patch doesn't enable tun zero-copy. tun will copy data It's not an issue now. We can disallow macvtap attach to bridge when zero-copy is enabled. > - SG support > - HIGHDMA support (on arches where this makes sense) This can be checked by device flags. > - no filtering based on data (data is mapped in guest) > - on fast path no calls to skb_copy, skb_clone, pskb_copy, > pskb_expand_head as these are slow Any calls to skb_copy, skb_clone, pskb_copy, pskb_expand_head will do a copy. The performance should be the same as none zero-copy case before. I have done/tested the patch V6, will send it out for review tomorrow. I am looking at where there are some cases, skb remains the same for filtering. > First 2 requirements are a must, all other requirements > are just dependencies to make sure zero copy will be faster > than non zero copy. > Using a new feature bit is probably the simplest approach to > this. macvtap on top of most physical NICs most likely works > correctly so it seems a bit more work than it needs to be, > but it's also the safest one I think ... For "macvtap/vhost zero-copy" we can use SG & HIGHDMA to enable it, it looks safe to me once patching skb_copy, skb_clone, pskb_copy, pskb_expand_head. To extend zero-copy in other usages, we can have a new feature bit later. Is that reasonable? Thanks Shirley