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.