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From: Eric Dumazet <eric.dumazet@gmail.com>
To: Daniel Borkmann <daniel@iogearbox.net>, ast@kernel.org
Cc: john.fastabend@gmail.com, kafai@fb.com, netdev@vger.kernel.org,
	bpf@vger.kernel.org, Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH bpf-next v4 2/6] bpf, net: rework cookie generator as per-cpu one
Date: Wed, 30 Sep 2020 17:55:55 +0200	[thread overview]
Message-ID: <c42aac64-d78c-7f3b-9e07-5da7d46aa582@gmail.com> (raw)
In-Reply-To: <8a80b8d27d3c49f9a14e1d5213c19d8be87d1dc8.1601477936.git.daniel@iogearbox.net>



On 9/30/20 5:18 PM, Daniel Borkmann wrote:
> With its use in BPF, the cookie generator can be called very frequently
> in particular when used out of cgroup v2 hooks (e.g. connect / sendmsg)
> and attached to the root cgroup, for example, when used in v1/v2 mixed
> environments. In particular, when there's a high churn on sockets in the
> system there can be many parallel requests to the bpf_get_socket_cookie()
> and bpf_get_netns_cookie() helpers which then cause contention on the
> atomic counter.
> 
> As similarly done in f991bd2e1421 ("fs: introduce a per-cpu last_ino
> allocator"), add a small helper library that both can use for the 64 bit
> counters. Given this can be called from different contexts, we also need
> to deal with potential nested calls even though in practice they are
> considered extremely rare. One idea as suggested by Eric Dumazet was
> to use a reverse counter for this situation since we don't expect 64 bit
> overflows anyways; that way, we can avoid bigger gaps in the 64 bit
> counter space compared to just batch-wise increase. Even on machines
> with small number of cores (e.g. 4) the cookie generation shrinks from
> min/max/med/avg (ns) of 22/50/40/38.9 down to 10/35/14/17.3 when run
> in parallel from multiple CPUs.
> 
> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
> Acked-by: Martin KaFai Lau <kafai@fb.com>
> Cc: Eric Dumazet <eric.dumazet@gmail.com>

Reviewed-by: Eric Dumazet <edumazet@google.com>

Thanks.


  reply	other threads:[~2020-09-30 15:56 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-30 15:18 [PATCH bpf-next v4 0/6] Various BPF helper improvements Daniel Borkmann
2020-09-30 15:18 ` [PATCH bpf-next v4 1/6] bpf: add classid helper only based on skb->sk Daniel Borkmann
2020-09-30 15:18 ` [PATCH bpf-next v4 2/6] bpf, net: rework cookie generator as per-cpu one Daniel Borkmann
2020-09-30 15:55   ` Eric Dumazet [this message]
2020-09-30 15:18 ` [PATCH bpf-next v4 3/6] bpf: add redirect_neigh helper as redirect drop-in Daniel Borkmann
2020-09-30 16:08   ` David Ahern
2020-09-30 20:56     ` Daniel Borkmann
2020-09-30 15:18 ` [PATCH bpf-next v4 4/6] bpf, libbpf: add bpf_tail_call_static helper for bpf programs Daniel Borkmann
2020-09-30 15:18 ` [PATCH bpf-next v4 5/6] bpf, selftests: use bpf_tail_call_static where appropriate Daniel Borkmann
2020-09-30 17:23   ` Martin KaFai Lau
2020-09-30 15:18 ` [PATCH bpf-next v4 6/6] bpf, selftests: add redirect_neigh selftest Daniel Borkmann
2020-09-30 17:31   ` Martin KaFai Lau
2020-09-30 19:20   ` Alexei Starovoitov
2020-09-30 21:01     ` Daniel Borkmann
2020-09-30 21:12       ` Alexei Starovoitov
2020-09-30 19:10 ` [PATCH bpf-next v4 0/6] Various BPF helper improvements patchwork-bot+bpf

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