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Message-ID: <9c9ef2228dfcb950b5c75382bd421c6169e547a0.camel@redhat.com>
Subject: Re: [PATCH net-next] tcp: add tcp_tx_skb_cache_key checking in
 sk_stream_alloc_skb()
From:   Paolo Abeni <pabeni@redhat.com>
To:     Yunsheng Lin <linyunsheng@huawei.com>, davem@davemloft.net,
        kuba@kernel.org, MPTCP Upstream <mptcp@lists.linux.dev>
Cc:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        linuxarm@openeuler.org, edumazet@google.com,
        yoshfuji@linux-ipv6.org, dsahern@kernel.org
Date:   Wed, 01 Sep 2021 12:52:05 +0200
In-Reply-To: <1630492744-60396-1-git-send-email-linyunsheng@huawei.com>
References: <1630492744-60396-1-git-send-email-linyunsheng@huawei.com>
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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.

Cheers,

Paolo