netdev - Re: [RFC PATCH v2 net-next 0/4] txhash: Make hash rethink configurable

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Message-Id: <82E7E49A-5EB9-4719-87FC-836718A031A9@yandex-team.ru>
Date:   Tue, 30 Nov 2021 12:58:03 +0300
From:   Akhmat Karakotov <hmukos@...dex-team.ru>
To:     hmukos@...dex-team.ru
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Alexander Azimov <mitradir@...dex-team.ru>,
        netdev@...r.kernel.org, tom@...bertland.com, zeil@...dex-team.ru,
        hmukos@...dex-team.ru
Subject: Re: [RFC PATCH v2 net-next 0/4] txhash: Make hash rethink
 configurable

Hi Eric,

I wonder if you have time to provide review regarding my last update to the patch.

> On Nov 23, 2021, at 16:20, Akhmat Karakotov <hmukos@...dex-team.ru> wrote:
> 
> Hi Eric,
> 
> I've sent v2 of the patch. I've removed confusing part with sysctl default values
> and made other changes according to your comments. I look forward for your
> review.
> 
>> On Nov 12, 2021, at 21:19, Akhmat Karakotov <hmukos@...dex-team.ru> wrote:
>> 
>> As it was shown in the report by Alexander Azimov, hash rethink at the
>> client-side may lead to connection timeout toward stateful anycast
>> services. Tom Herbert created a patchset to address this issue by applying
>> hash rethink only after a negative routing event (3RTOs) [1]. This change
>> also affects server-side behavior, which we found undesirable. This
>> patchset changes defaults in a way to make them safe: hash rethink at the
>> client-side is disabled and enabled at the server-side upon each RTO
>> event or in case of duplicate acknowledgments.
>> 
>> This patchset provides two options to change default behaviour. The hash
>> rethink may be disabled at the server-side by the new sysctl option.
>> Changes in the sysctl option don't affect default behavior at the
>> client-side.
>> 
>> Hash rethink can also be enabled/disabled with socket option or bpf
>> syscalls which ovewrite both default and sysctl settings. This socket
>> option is available on both client and server-side. This should provide
>> mechanics to enable hash rethink inside administrative domain, such as DC,
>> where hash rethink at the client-side can be desirable.
>> 
>> [1] https://lore.kernel.org/netdev/20210809185314.38187-1-tom@herbertland.com/
>> 
>> v2:
>> 	- Changed sysctl default to ENABLED in all patches. Reduced sysctl
>> 	  and socket option size to u8. Fixed netns bug reported by kernel
>> 	  test robot.
>> 
>> Akhmat Karakotov (4):
>> txhash: Make rethinking txhash behavior configurable via sysctl
>> txhash: Add socket option to control TX hash rethink behavior
>> bpf: Add SO_TXREHASH setsockopt
>> tcp: change SYN ACK retransmit behaviour to account for rehash
>> 
>> arch/alpha/include/uapi/asm/socket.h  |  2 ++
>> arch/mips/include/uapi/asm/socket.h   |  2 ++
>> arch/parisc/include/uapi/asm/socket.h |  2 ++
>> arch/sparc/include/uapi/asm/socket.h  |  2 ++
>> include/net/netns/core.h              |  1 +
>> include/net/sock.h                    | 28 ++++++++++++++-------------
>> include/uapi/asm-generic/socket.h     |  2 ++
>> include/uapi/linux/socket.h           |  4 ++++
>> net/core/filter.c                     | 10 ++++++++++
>> net/core/net_namespace.c              |  2 ++
>> net/core/sock.c                       | 13 +++++++++++++
>> net/core/sysctl_net_core.c            | 15 ++++++++++++--
>> net/ipv4/inet_connection_sock.c       |  3 +++
>> net/ipv4/tcp_output.c                 |  3 ++-
>> 14 files changed, 73 insertions(+), 16 deletions(-)
>> 
>> -- 
>> 2.17.1
>> 
>