Re: [PATCH v2 net-next 0/7] net_sched: act: lockless operation

On Mon, Jul 6, 2015 at 2:12 PM, Jamal Hadi Salim [off-list ref] wrote:

on mirred:
The main thing that is read-write is the stats. lastuse timestamp
as well, but that one doesnt have to be accurate (used mainly
to help decide when to flush out policies). so the lock around
all that code is not necessary.

BTW: I was wondering based on what you said earlier on false sharing
if tcf_common can be re-arranged to avoid that?

Not really : You would still have a stall on lastuse ultimately, even
if it sits in a cache line of its own.

I mentioned that it shared a cache line to explain with "perf" was
showing the stall on reading another field.

For mirred, you may have to add for overlimit stat in the common
structure (we should really increment drop stats when we return
TC_ACT_SHOT).

Having said that: we want to maintain the fact that an action
instance (based on index) can be used across different policies.
i dont see any issue with the way you are proceeding for that
to continue to work. i.e i can say something like:
- create an action to redirect or mirror to port blah index 10
- create filter one on eth1 with 1 of the actions being mirred index 10
- create filter two on eth0 with 1 of the actions being mirred index 10

I do not see any issues either.

On IFB:
we use tasklets originally to avoid re-ordering. I think tasklets would
still be useful to keep, with each tied to a queue?

Sure. We do not care about reorders if packets were delivered to
different RX queues.