netdev - Re: [PATCH v2 net-next] net: neigh: add netlink filtering based on LLADDR for dump

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Date:   Thu, 9 Jun 2022 09:58:45 +0200
From:   Florent Fourcot <florent.fourcot@...irst.fr>
To:     David Ahern <dsahern@...nel.org>,
        Florent Fourcot <florent.fourcot@...irst.fr>,
        netdev@...r.kernel.org
Cc:     Eric Dumazet <edumazet@...gle.com>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH v2 net-next] net: neigh: add netlink filtering based on
 LLADDR for dump

Hello David,

> 
> Kernel side filtering has always been kept to simple, coarse grained
> checks - like a device index or upper device index. It's a fine line
> managing kernel cycles holding the rtnl vs cycles shipping the data to
> userspace. e.g., a memcmp has a higher cost than a dev->index
> comparison. I see the point about GET only - potential for many matches
> and a lookup of the ll address is basically a filtered dump. Mixed
> thoughts on whether this should be merged.

Thanks for your feedback. As you know, this option will not slow down 
standard dump.

I understand your concern, but the choice is between:
  * putting all entries on socket to send data to userspace. It means 
several memcpy (at least one for L3 address, one for L2 address) for 
each entries
  * Use proposed filter, with a single memcmp. memcpy is not called for 
filtered out entries.

My solution looks faster, but I can send a v3 with some numbers if you 
think that it's important to get this patch merged.


Best regards,

-- 
Florent Fourcot

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