Messages in this thread | | | Date | Wed, 19 Feb 2014 19:13:08 +0000 | From | Zoltan Kiss <> | Subject | Re: [RFC v2 2/4] net: enables interface option to skip IP |
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On 19/02/14 17:20, Luis R. Rodriguez wrote: > On Wed, Feb 19, 2014 at 8:45 AM, Dan Williams <dcbw@redhat.com> wrote: >> On Tue, 2014-02-18 at 13:19 -0800, Luis R. Rodriguez wrote: >>> On Mon, Feb 17, 2014 at 12:23 PM, Dan Williams <dcbw@redhat.com> wrote: >>>> On Fri, 2014-02-14 at 18:59 -0800, Luis R. Rodriguez wrote: >>>>> From: "Luis R. Rodriguez" <mcgrof@suse.com> >>>>> >>>>> Some interfaces do not need to have any IPv4 or IPv6 >>>>> addresses, so enable an option to specify this. One >>>>> example where this is observed are virtualization >>>>> backend interfaces which just use the net_device >>>>> constructs to help with their respective frontends. >>>>> >>>>> This should optimize boot time and complexity on >>>>> virtualization environments for each backend interface >>>>> while also avoiding triggering SLAAC and DAD, which is >>>>> simply pointless for these type of interfaces. >>>> >>>> Would it not be better/cleaner to use disable_ipv6 and then add a >>>> disable_ipv4 sysctl, then use those with that interface? >>> >>> Sure, but note that the both disable_ipv6 and accept_dada sysctl >>> parameters are global. ipv4 and ipv6 interfaces are created upon >>> NETDEVICE_REGISTER, which will get triggered when a driver calls >>> register_netdev(). The goal of this patch was to enable an early >>> optimization for drivers that have no need ever for ipv4 or ipv6 >>> interfaces. >> >> Each interface gets override sysctls too though, eg: >> >> /proc/sys/net/ipv6/conf/enp0s25/disable_ipv6 > > I hadn't seen those, thanks! > >> which is the one I meant; you're obviously right that the global ones >> aren't what you want here. But the specific ones should be suitable? > > Under the approach Stephen mentioned by first ensuring the interface > is down yes. There's one use case I can consider to still want the > patch though, more on that below. > >> If you set that on a per-interface basis, then you'll get EPERM or >> something whenever you try to add IPv6 addresses or do IPv6 routing. > > Neat, thanks. > >>> Zoltan has noted though some use cases of IPv4 or IPv6 addresses on >>> backends though, as such this is no longer applicable as a >>> requirement. The ipv4 sysctl however still seems like a reasonable >>> approach to enable optimizations of the network in topologies where >>> its known we won't need them but -- we'd need to consider a much more >>> granular solution, not just global as it is now for disable_ipv6, and >>> we'd also have to figure out a clean way to do this to not incur the >>> cost of early address interface addition upon register_netdev(). >>> >>> Given that we have a use case for ipv4 and ipv6 addresses on >>> xen-netback we no longer have an immediate use case for such early >>> optimization primitives though, so I'll drop this. >>> >>>> The IFF_SKIP_IP seems to duplicate at least part of what disable_ipv6 is >>>> already doing. >>> >>> disable_ipv6 is global, the goal was to make this granular and skip >>> the cost upon early boot, but its been clarified we don't need this. >> >> Like Stephen says, you need to make sure you set them before IFF_UP, but >> beyond that, wouldn't the interface-specific sysctls work? > > Yeah that'll do it, unless there is a measurable run time benefit cost > to never even add these in the first place. Consider a host with tons > of guests, not sure how many is 'a lot' these days. One would have to > measure the cost of reducing the amount of time it takes to boot these > up. As discussed in the other threads though there *is* some use cases > of assigning IPv4 or IPv6 addresses to the backend interfaces though: > routing them (although its unclear to me if iptables can be used > instead, Zoltan?).
Not with OVS, it steals the packet before netfilter hooks.
Zoli
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