From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jiri Pirko Subject: Re: [net-next PATCH 3/4] net: sched: cls_u32 add bit to specify software only rules Date: Wed, 24 Feb 2016 09:40:57 +0100 Message-ID: <20160224084057.GC2151@nanopsycho.orion> References: <20160223190233.5970.61226.stgit@john-Precision-Tower-5810> <20160223190321.5970.58924.stgit@john-Precision-Tower-5810> <20160224080440.GA26500@office.Home> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: John Fastabend , daniel@iogearbox.net, netdev@vger.kernel.org, alexei.starovoitov@gmail.com, davem@davemloft.net, jhs@mojatatu.com To: "Amir Vadai\"" Return-path: Received: from mail-wm0-f44.google.com ([74.125.82.44]:33829 "EHLO mail-wm0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758195AbcBXIk7 (ORCPT ); Wed, 24 Feb 2016 03:40:59 -0500 Received: by mail-wm0-f44.google.com with SMTP id b205so24689041wmb.1 for ; Wed, 24 Feb 2016 00:40:59 -0800 (PST) Content-Disposition: inline In-Reply-To: <20160224080440.GA26500@office.Home> Sender: netdev-owner@vger.kernel.org List-ID: Wed, Feb 24, 2016 at 09:04:40AM CET, amir@vadai.me wrote: >On Tue, Feb 23, 2016 at 11:03:21AM -0800, John Fastabend wrote: >> In the initial implementation the only way to stop a rule from being >> inserted into the hardware table was via the device feature flag. >> However this doesn't work well when working on an end host system >> where packets are expect to hit both the hardware and software >> datapaths. >> >> For example we can imagine a rule that will match an IP address and >> increment a field. If we install this rule in both hardware and >> software we may increment the field twice. To date we have only >> added support for the drop action so we have been able to ignore >> these cases. But as we extend the action support we will hit this >> example plus more such cases. Arguably these are not even corner >> cases in many working systems these cases will be common. >> >> To avoid forcing the driver to always abort (i.e. the above example) >> this patch adds a flag to add a rule in software only. A careful >> user can use this flag to build software and hardware datapaths >> that work together. One example we have found particularly useful >> is to use hardware resources to set the skb->mark on the skb when >> the match may be expensive to run in software but a mark lookup >> in a hash table is cheap. The idea here is hardware can do in one >> lookup what the u32 classifier may need to traverse multiple lists >> and hash tables to compute. The flag is only passed down on inserts >> on deletion to avoid stale references in hardware we always try >> to remove a rule if it exists. >> >> Notice we do not add a hardware only case here. If you were to >> add a hardware only case then you are stuck with the problem >> of where to stick the software representation of that filter >> rule. If its stuck on the same filter list as the software only and >> software/hardware rules it then has to be walked over and ignored >> in the classify path. The overhead is not huge but is measurable. >> And with so much work being invested in speeding up rx/tx of >> pkt processing this is unacceptable IMO. The other option is to >> have a special hook just for hardware only resources. This is >> implemented in the next patch. >> >> Signed-off-by: John Fastabend > >[...] > >> >> -static bool u32_should_offload(struct net_device *dev) >> +static bool u32_should_offload(struct net_device *dev, u32 flags) >> { >> if (!(dev->features & NETIF_F_HW_TC)) >> return false; >> >> - return dev->netdev_ops->ndo_setup_tc; >> + if (flags & TCA_U32_FLAGS_SOFTWARE) >> + return false; >> + >> + if (!dev->netdev_ops->ndo_setup_tc) >> + return false; >> + >> + return true; >> } >This function and flag should be a generic filter attribute - not just >u32. I agree, this should be generic. Regarding flags attr, we have the same situation as with other common attrs: TCA_U32_POLICE TCA_FLOW_POLICE TCA_CGROUP_POLICE TCA_BPF_POLICE TCA_U32_ACT TCA_FLOW_ACT TCA_CGROUP_ACT TCA_BPF_ACT TCA_FLOWER_ACT I guess we have no other choice then to have TCA_U32_FLAGS TCA_FLOWER_FLAGS etc :(