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

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Message-ID: <5e15504b79ddb_68832ae93d7145c063@john-XPS-13-9370.notmuch>
Date:   Tue, 07 Jan 2020 19:45:15 -0800
From:   John Fastabend <john.fastabend@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>,
        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

Toke Høiland-Jørgensen wrote:
> 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
> 

Ah I was just catching up with email and missed itwas already applied.

I can also submit a few fixup patches no problem for the comments and this.

.John