From: Eric Dumazet <edumazet@google.com>
To: Paolo Abeni <pabeni@redhat.com>
Cc: Yunsheng Lin <linyunsheng@huawei.com>,
David Miller <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
MPTCP Upstream <mptcp@lists.linux.dev>,
netdev <netdev@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
linuxarm@openeuler.org,
Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
David Ahern <dsahern@kernel.org>
Subject: Re: [PATCH net-next] tcp: add tcp_tx_skb_cache_key checking in sk_stream_alloc_skb()
Date: Wed, 1 Sep 2021 08:06:52 -0700 [thread overview]
Message-ID: <CANn89iJFeM=DgcQpDbaE38uhxTEL6REMWPnVFt7Am7Nuf4wpMw@mail.gmail.com> (raw)
In-Reply-To: <9c9ef2228dfcb950b5c75382bd421c6169e547a0.camel@redhat.com>
On Wed, Sep 1, 2021 at 3:52 AM Paolo Abeni <pabeni@redhat.com> wrote:
>
> On Wed, 2021-09-01 at 18:39 +0800, Yunsheng Lin wrote:
> > Since tcp_tx_skb_cache is disabled by default in:
> > commit 0b7d7f6b2208 ("tcp: add tcp_tx_skb_cache sysctl")
> >
> > Add tcp_tx_skb_cache_key checking in sk_stream_alloc_skb() to
> > avoid possible branch-misses.
> >
> > Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
>
> Note that MPTCP is currently exploiting sk->sk_tx_skb_cache. If we get
> this patch goes in as-is, it will break mptcp.
>
> One possible solution would be to let mptcp usage enable sk-
> >sk_tx_skb_cache, but that has relevant side effects on plain TCP.
>
> Another options would be re-work once again the mptcp xmit path to
> avoid using sk->sk_tx_skb_cache.
>
Hmmm, I actually wrote a revert of this feature but forgot to submit
it last year.
commit c36cfbd791f62c0f7c6b32132af59dfdbe6be21b (HEAD -> listener_scale4)
Author: Eric Dumazet <edumazet@google.com>
Date: Wed May 20 06:38:38 2020 -0700
tcp: remove sk_{tr}x_skb_cache
This reverts the following patches :
2e05fcae83c41eb2df10558338dc600dc783af47 ("tcp: fix compile error
if !CONFIG_SYSCTL")
4f661542a40217713f2cee0bb6678fbb30d9d367 ("tcp: fix zerocopy and
notsent_lowat issues")
472c2e07eef045145bc1493cc94a01c87140780a ("tcp: add one skb cache for tx")
8b27dae5a2e89a61c46c6dbc76c040c0e6d0ed4c ("tcp: add one skb cache for rx")
Having a cache of one skb (in each direction) per TCP socket is fragile,
since it can cause a significant increase of memory needs,
and not good enough for high speed flows anyway where more than one skb
is needed.
We want instead to add a generic infrastructure, with more flexible per-cpu
caches, for alien NUMA nodes.
Signed-off-by: Eric Dumazet <edumazet@google.com>
I will update this commit to also remove the part in MPTCP.
Let's remove this feature and replace it with something less costly.
next prev parent reply other threads:[~2021-09-01 15:07 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-01 10:39 [PATCH net-next] tcp: add tcp_tx_skb_cache_key checking in sk_stream_alloc_skb() Yunsheng Lin
2021-09-01 10:52 ` Paolo Abeni
2021-09-01 10:52 ` Paolo Abeni
2021-09-01 15:06 ` Eric Dumazet [this message]
2021-09-01 15:06 ` Eric Dumazet
2021-09-01 15:16 ` Eric Dumazet
2021-09-01 15:16 ` Eric Dumazet
2021-09-01 15:25 ` Paolo Abeni
2021-09-01 15:25 ` Paolo Abeni
2021-09-01 15:29 ` Eric Dumazet
2021-09-01 15:29 ` Eric Dumazet
2021-09-01 16:01 ` Paolo Abeni
2021-09-01 16:01 ` Paolo Abeni
2021-09-01 16:02 ` Eric Dumazet
2021-09-01 16:02 ` Eric Dumazet
2021-09-02 0:47 ` Yunsheng Lin
2021-09-02 1:13 ` Eric Dumazet
2021-09-02 2:05 ` Yunsheng Lin
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