Re: [RFC PATCH v2 net-next 00/15] tc-taprio offload for SJA1105 DSA

On Sat, 31 Aug 2019 at 01:29, Jakub Kicinski
[off-list ref] wrote:

On Fri, 30 Aug 2019 13:11:11 +0300, Vladimir Oltean wrote:

quoted

On Fri, 30 Aug 2019 at 04:21, Jakub Kicinski wrote:

quoted

On Fri, 30 Aug 2019 03:46:20 +0300, Vladimir Oltean wrote:

quoted

- Configuring the switch over SPI cannot apparently be done from this
  ndo_setup_tc callback because it runs in atomic context. I also have
  some downstream patches to offload tc clsact matchall with mirred
  action, but in that case it looks like the atomic context restriction
  does not apply.

This sounds really surprising ndo_setup_tc should always be allowed to
sleep. Can the taprio limitation be lifted somehow?

I need to get more familiar with the taprio internal data structures.
I think you're suggesting to get those updated to a consistent state
while under spin_lock_bh(qdisc_lock(sch)), then call ndo_setup_tc from
outside that critical section?

I'm not 100% sure how taprio handles locking TBH, it just seems naive
that HW callback will not need to sleep, so the kernel should make sure
that callback can sleep. Otherwise we'll end up with 3/4 of drivers
implementing some async work routine...

Sorry, I know that's quite general and not that helpful.

quoted

Also, I just noticed that I introduced a bug in taprio_disable_offload
with my reference counting addition. The qdisc can't just pass stack
memory to the driver, now that it's allowing it to keep it. So
definitely the patch needs more refactoring.

Ah, a slight deja vu, I think someone else has done it in the past :)

Ok, I think I managed to move the ndo_setup_tc callback outside of
atomic context and nothing broke so far... Any other comments or
should I go ahead and send a first proper patchset?

Thanks,
-Vladimir