Messages in this thread | | | Date | Mon, 24 Oct 2022 17:39:13 +0200 | From | Ilya Maximets <> | Subject | Re: [RFE net-next] net: tun: 1000x speed up |
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On 10/24/22 14:27, Nicolas Dichtel wrote: > Le 24/10/2022 à 13:56, Ilya Maximets a écrit : >> On 10/24/22 11:44, Nicolas Dichtel wrote: >>> Le 21/10/2022 à 18:07, Jakub Kicinski a écrit : >>>> On Fri, 21 Oct 2022 13:49:21 +0200 Ilya Maximets wrote: >>>>> Bump the advertised speed to at least match the veth. 10Gbps also >>>>> seems like a more or less fair assumption these days, even though >>>>> CPUs can do more. Alternative might be to explicitly report UNKNOWN >>>>> and let the application/user decide on a right value for them. >>>> >>>> UNKOWN would seem more appropriate but at this point someone may depend >>>> on the speed being populated so it could cause regressions, I fear :S >>> If it is put in a bonding, it may cause some trouble. Maybe worth than >>> advertising 10M. >> >> My thoughts were that changing the number should have a minimal impact >> while changing it to not report any number may cause some issues in >> applications that doesn't expect that for some reason (not having a >> fallback in case reported speed is unknown isn't great, and the argument >> can be made that applications should check that, but it's hard to tell >> for every application if they actually do that today). >> >> Bonding is also a good point indeed, since it's even in-kernel user. >> >> >> The speed bump doesn't solve the problem per se. It kind of postpones >> the decision, since we will run into the same issue eventually again. >> That's why I wanted to discuss that first. >> >> Though I think that at least unification across virtual devices (tun and >> veth) should be a step in a right direction. > Just to make it clear, I'm not against aligning speed with veth, I'm only > against reporting UNKNOWN.
Ack. Thanks for the clarification!
> >> >>> >>> Note that this value could be configured with ethtool: >>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=4e24f2dd516ed >> >> This is interesting, but it's a bit hard to manage, because in order >> to make a decision to bump the speed, application should already know >> that this is a tun/tap device. So, there has to be a special case > But this should be done by the application which creates this tun interface. Not > by the application that uses this information. > >> implemented in the code that detects the driver and changes the speed >> (this is about application that is using the interface, but didn't >> create it), but if we already know the driver, then it doesn't make >> sense to actually change the speed in many cases as application can >> already act accordingly. >> >> Also, the application may not have permissions to do that (I didn't >> check the requirements, but my guess would be at least CAP_NET_ADMIN?). > Sure, but the one who creates it, has the right to configure it correctly. It's > part of the configuration of the interface. I mostly agree with that, but that still means changing userspace applications. I'm pretty sure very little number of applications, if any at all, do that today.
> > Setting an higher default speed seems to be a workaround to fix an incorrect > configuration. And as you said, it will probably be wrong again in a few years ;-)
Yep.
Workarounds do exist today. For example, if you specify max-rate in QoS configuration for OVS, it will not use the link speed as a reference at all. I'm just not sure if replacing one workaround with another workaround is a good option. Especially because that will require changing userspace applications and the problem itself is kind of artificial.
> >> >> For the human user it's still one extra configuration step that they >> need to remember to perform. > I don't buy this argument. There are already several steps: creating and > configuring an interface requires more than one command.
Muscle memory, I guess. :) But yes, might not be a huge deal for human users, I agree.
It's more of a concern for multi-layer systems where actual interfaces are created somewhere deep inside the software stack and actual humans don't really perform these commands by hands.
Best regards, Ilya Maximets.
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