RE: [PATCH bpf-next v2 7/8] xdp: remove map_to_flush and map swap detection

Toke Høiland-Jørgensen
2020-01-07T21:07:26Z

John Fastabend <john.fastabend@gmail.com> writes:

> Björn Töpel wrote:
>> From: Björn Töpel <bjorn.topel@intel.com>
>>
>> Now that all XDP maps that can be used with bpf_redirect_map() tracks
>> entries to be flushed in a global fashion, there is not need to track
>> that the map has changed and flush from xdp_do_generic_map()
>> anymore. All entries will be flushed in xdp_do_flush_map().
>>
>> This means that the map_to_flush can be removed, and the corresponding
>> checks. Moving the flush logic to one place, xdp_do_flush_map(), give
>> a bulking behavior and performance boost.
>>
>> Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
>> Signed-off-by: Björn Töpel <bjorn.topel@intel.com>
>> ---
>
> __dev_map_flush() still has rcu_read_lock/unlock() around flush_list by
> this point, assuming I've followed along correctly. Can we drop those
> now seeing its per CPU and all list ops are per-cpu inside napi context?

Hmm, I guess so? :)

> Two reasons to consider, with this patch dev_map_flush() is always
> called even if the list is empty so even in TX case without redirect.
> But probably more important it makes the locking requirements more clear.
> Could probably be done in a follow up patch but wanted to bring it up.

This series was already merged, but I'll follow up with the non-map
redirect change. This requires a bit of refactoring anyway, so I can
incorporate the lock removal into that...

-Toke