> -----Original Message----- > From: Neal Cardwell <ncardw...@google.com> > Sent: Tuesday, October 10, 2023 4:07 PM > To: Haiyang Zhang <haiya...@microsoft.com> > Cc: linux-hyp...@vger.kernel.org; net...@vger.kernel.org; KY Srinivasan > <k...@microsoft.com>; da...@davemloft.net; eduma...@google.com; > k...@kernel.org; pab...@redhat.com; cor...@lwn.net; > dsah...@kernel.org; ych...@google.com; kun...@amazon.com; > morl...@google.com; mfree...@cloudflare.com; mubash...@google.com; > linux-doc@vger.kernel.org; wei...@google.com; linux- > ker...@vger.kernel.org > Subject: Re: [PATCH net-next,v2] tcp: Set pingpong threshold via sysctl > > [You don't often get email from ncardw...@google.com. Learn why this is > important at https://aka.ms/LearnAboutSenderIdentification ] > > On Tue, Oct 10, 2023 at 3:24 PM Haiyang Zhang <haiya...@microsoft.com> > wrote: > > > > TCP pingpong threshold is 1 by default. But some applications, like SQL DB > > may prefer a higher pingpong threshold to activate delayed acks in quick > > ack mode for better performance. > > > > The pingpong threshold and related code were changed to 3 in the year > > 2019 in: > > commit 4a41f453bedf ("tcp: change pingpong threshold to 3") > > And reverted to 1 in the year 2022 in: > > commit 4d8f24eeedc5 ("Revert "tcp: change pingpong threshold to 3"") > > > > There is no single value that fits all applications. > > Add net.ipv4.tcp_pingpong_thresh sysctl tunable, so it can be tuned for > > optimal performance based on the application needs. > > > > Signed-off-by: Haiyang Zhang <haiya...@microsoft.com> > > --- > > v2: Make it per-namesapce setting, and other updates suggested by Neal > Cardwell, > > and Kuniyuki Iwashima. > > > > --- > > Documentation/networking/ip-sysctl.rst | 8 ++++++++ > > include/net/inet_connection_sock.h | 16 ++++++++++++---- > > include/net/netns/ipv4.h | 1 + > > net/ipv4/sysctl_net_ipv4.c | 8 ++++++++ > > net/ipv4/tcp_ipv4.c | 2 ++ > > net/ipv4/tcp_output.c | 4 ++-- > > 6 files changed, 33 insertions(+), 6 deletions(-) > > > > diff --git a/Documentation/networking/ip-sysctl.rst > b/Documentation/networking/ip-sysctl.rst > > index 5bfa1837968c..c0308b65dc2f 100644 > > --- a/Documentation/networking/ip-sysctl.rst > > +++ b/Documentation/networking/ip-sysctl.rst > > @@ -1183,6 +1183,14 @@ tcp_plb_cong_thresh - INTEGER > > > > Default: 128 > > > > +tcp_pingpong_thresh - INTEGER > > + TCP pingpong threshold is 1 by default, but some application may > > need > a > > + higher threshold for optimal performance. > > + > > + Possible Values: 1 - 255 > > + > > + Default: 1 > > + > > It would be good to document what the meaning of the parameter is. > Perhaps consider something like: > > 'The number of estimated data replies sent for estimated incoming data > requests that must happen before TCP estimates that a connection is a > "ping-pong" (request-response) connection for which delayed > acknowledgments can provide benefits. This threshold is 1 by default, > but some applications may need a higher threshold for optimal > performance.' > Will do.
Thanks, - Haiyang
