On Tue, Jan 19, 2021 at 02:22:55PM -0800, Jakub Kicinski wrote: > On Sun, 17 Jan 2021 10:02:18 +0200 Ido Schimmel wrote: > > From: Ido Schimmel <ido...@nvidia.com> > > > > The RED qdisc currently supports two qevents: "early_drop" and "mark". The > > filters added to the block bound to the "early_drop" qevent are executed on > > packets for which the RED algorithm decides that they should be > > early-dropped. The "mark" filters are similarly executed on ECT packets > > that are marked as ECN-CE (Congestion Encountered). > > > > A previous patchset has offloaded "early_drop" filters on Spectrum-2 and > > later, provided that the classifier used is "matchall", that the action > > used is either "trap" or "mirred", and a handful or further limitations. > > For early_drop trap or mirred makes obvious sense, no explanation > needed. > > But for marked as a user I'd like to see a _copy_ of the packet, > while the original continues on its marry way to the destination. > I'd venture to say that e.g. for a DCTCP deployment mark+trap is > unusable, at least for tracing, because it distorts the operation > by effectively dropping instead of marking. > > Am I reading this right?
You get a copy of the packet as otherwise it will create a lot of problems (like you wrote). > > If that is the case and you really want to keep the mark+trap > functionality - I feel like at least better documentation is needed. > The current two liner should also be rewritten, quoting from patch 1: > > > * - ``ecn_mark`` > > - ``drop`` > > - Traps ECN-capable packets that were marked with CE (Congestion > > Encountered) code point by RED algorithm instead of being dropped > > That needs to say that the trap is for datagrams trapped by a qevent. > Otherwise "Traps ... instead of being dropped" is too much of a > thought-shortcut, marked packets are not dropped. > > (I'd also think that trap is better documented next to early_drop, > let's look at it from the reader's perspective) How about: "Traps a copy of ECN-capable packets that were marked with CE (Congestion Encountered) code point by RED algorithm instead of being dropped. The trap is enabled by attaching a filter with action 'trap' to the 'mark' qevent of the RED qdisc." In addition, this output: $ devlink trap show pci/0000:06:00.0 trap ecn_mark pci/0000:06:00.0: name ecn_mark type drop generic true action trap group buffer_drops Can be converted to: $ devlink trap show pci/0000:06:00.0 trap ecn_mark pci/0000:06:00.0: name ecn_mark type drop generic true action mirror group buffer_drops "mirror: The packet is forwarded by the underlying device and a copy is sent to the CPU." In this case the action is static and you cannot change it.
