netdev - RE: [PATCH bpf-next v2 7/8] xdp: remove map_to

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Message-ID: <87imlnht6k.fsf@toke.dk>
Date:   Tue, 07 Jan 2020 22:07:15 +0100
From:   Toke Høiland-Jørgensen <toke@...hat.com>
To:     John Fastabend <john.fastabend@...il.com>,
        Björn Töpel 
        <bjorn.topel@...il.com>, netdev@...r.kernel.org, ast@...nel.org,
        daniel@...earbox.net
Cc:     Björn Töpel <bjorn.topel@...el.com>,
        bpf@...r.kernel.org, davem@...emloft.net,
        jakub.kicinski@...ronome.com, hawk@...nel.org,
        john.fastabend@...il.com, magnus.karlsson@...el.com,
        jonathan.lemon@...il.com
Subject: RE: [PATCH bpf-next v2 7/8] xdp: remove map_to_flush and map swap detection

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

> Björn Töpel wrote:
>> From: Björn Töpel <bjorn.topel@...el.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@...hat.com>
>> Signed-off-by: Björn Töpel <bjorn.topel@...el.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