netdev - Re: [PATCH net-next] sched: cls: enable verbose logging

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Date:   Tue, 15 May 2018 12:43:29 -0700
From:   Jakub Kicinski <kubakici@...pl>
To:     Cong Wang <xiyou.wangcong@...il.com>
Cc:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        David Ahern <dsahern@...il.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Jiri Pirko <jiri@...nulli.us>,
        Alexander Aring <aring@...atatu.com>,
        Jamal Hadi Salim <jhs@...atatu.com>
Subject: Re: [PATCH net-next] sched: cls: enable verbose logging

On Mon, 14 May 2018 22:31:46 -0700, Cong Wang wrote:
> On Mon, May 14, 2018 at 1:47 PM, Marcelo Ricardo Leitner wrote:
> > On Mon, May 14, 2018 at 01:30:53PM -0700, Cong Wang wrote:  
> >> On Sun, May 13, 2018 at 1:44 PM, Marcelo Ricardo Leitner wrote:  
> >> > Currently, when the rule is not to be exclusively executed by the
> >> > hardware, extack is not passed along and offloading failures don't
> >> > get logged. The idea was that hardware failures are okay because the
> >> > rule will get executed in software then and this way it doesn't confuse
> >> > unware users.
> >> >
> >> > But this is not helpful in case one needs to understand why a certain
> >> > rule failed to get offloaded. Considering it may have been a temporary
> >> > failure, like resources exceeded or so, reproducing it later and knowing
> >> > that it is triggering the same reason may be challenging.  
> >>
> >> I fail to understand why you need a flag here, IOW, why not just pass
> >> extack unconditionally?  
> >
> > Because (as discussed in the RFC[1], should have linked it here) it
> > could confuse users that are not aware of offloading and, in other
> > cases, it can be just noise (like it would be right now for ebpf,
> > which is mostly used in sw-path).
> >
> > 1.https://www.mail-archive.com/netdev@vger.kernel.org/msg223016.html  
> 
> My point is that a TC filter flag should be used for a filter attribute,
> logging is apparently not a part of filter. At least, put it into HW offloading,
> not in TC filter.
> 
> I know DaveM hates module parameters, but a module parameter here
> is more suitable than a TC filter flag.

Do you mean we should add a global cls_flower parameter to enable
verbose HW offload messages?  I'm not sure where "HW offloading" is.

I agree with you in principle, this could be made a "per application
context" flag.  Perhaps to be set on the socket.  But our existing
flags are per-request so it makes sense to do the same here IMHO.