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

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Message-ID: <5e14caaaab6f7_67962afd051fc5c06f@john-XPS-13-9370.notmuch>
Date:   Tue, 07 Jan 2020 10:15:06 -0800
From:   John Fastabend <john.fastabend@...il.com>
To:     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,
        Toke Høiland-Jørgensen <toke@...hat.com>
Subject: RE: [PATCH bpf-next v2 7/8] xdp: remove map_to_flush and map swap
 detection

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?

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.