On Fri, Nov 27, 2020 at 03:56:49PM -0800, Jakub Kicinski wrote: > What is it with my email today, didn't get this one again. > > On Sat, 28 Nov 2020 01:39:16 +0200 Vladimir Oltean wrote: > > On Sat, Nov 28, 2020 at 12:30:48AM +0100, Andrew Lunn wrote: > > > > If there is a better alternative I'm all ears but having /proc and > > > > ifconfig return zeros for error counts while ip link doesn't will lead > > > > to too much confusion IMO. While delayed update of stats is a fact of > > > > life for _years_ now (hence it was backed into the ethtool -C API). > > > > > > How about dev_seq_start() issues a netdev notifier chain event, asking > > > devices which care to update their cached rtnl_link_stats64 counters. > > > They can decide if their cache is too old, and do a blocking read for > > > new values. > > Just to avoid breaking the suggestion that seqfiles don't sleep after > .start? Hm. I thought BPF slept (or did cond_reshed()) in the middle of > seq iteration. We should double check that seqfiles really can't sleep. I don't think that seqfiles must not sleep after start(), at least that's my interpretation and confirmed by some tests. I added a might_sleep() in quite a few places and there is no issue now that we don't take the RCU read-side lock any longer. Have you seen my previous reply to George: | > I suppose it doesn't really matter though since the documentation says | > we can't sleep. | | You're talking, I suppose, about these words of wisdom in | Documentation/filesystems/seq_file.rst? | | | However, the seq_file code (by design) will not sleep between the calls | | to start() and stop(), so holding a lock during that time is a | | reasonable thing to do. The seq_file code will also avoid taking any | | other locks while the iterator is active. | | It _doesn't_ say that you can't sleep between start() and stop(), right? | It just says that if you want to keep the seq_file iterator atomic, the | seq_file code is not sabotaging you by sleeping. But you still could | sleep if you wanted to.
