From: Herbert Xu <herbert@gondor.apana.org.au>
To: Eric Dumazet <edumazet@google.com>
Cc: Olof Johansson <olof@lixom.net>,
David Miller <davem@davemloft.net>,
Neil Horman <nhorman@tuxdriver.com>,
Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>,
Vladislav Yasevich <vyasevich@gmail.com>,
Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
linux-crypto@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
linux-sctp@vger.kernel.org, netdev <netdev@vger.kernel.org>,
linux-decnet-user@lists.sourceforge.net,
kernel-team <kernel-team@fb.com>
Subject: Re: [PATCH] net/sock: move memory_allocated over to percpu_counter variables
Date: Fri, 7 Sep 2018 11:32:57 +0800 [thread overview]
Message-ID: <20180907033257.2nlgiqm2t4jiwhzc@gondor.apana.org.au> (raw)
In-Reply-To: <CANn89i+akEWrHELBkZJQOxok-ZfYy+FNPUWdPEfB6c4YyWLqJA@mail.gmail.com>
On Thu, Sep 06, 2018 at 12:33:58PM -0700, Eric Dumazet wrote:
> On Thu, Sep 6, 2018 at 12:21 PM Olof Johansson <olof@lixom.net> wrote:
> >
> > Today these are all global shared variables per protocol, and in
> > particular tcp_memory_allocated can get hot on a system with
> > large number of CPUs and a substantial number of connections.
> >
> > Moving it over to a per-cpu variable makes it significantly cheaper,
> > and the added overhead when summing up the percpu copies is still smaller
> > than the cost of having a hot cacheline bouncing around.
>
> I am curious. We never noticed contention on this variable, at least for TCP.
Yes these variables are heavily amortised so I'm surprised that
they would cause much contention.
> Please share some numbers with us.
Indeed.
Thanks,
--
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
next prev parent reply other threads:[~2018-09-07 3:33 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-06 19:20 [PATCH] net/sock: move memory_allocated over to percpu_counter variables Olof Johansson
2018-09-06 19:33 ` Eric Dumazet
2018-09-07 3:32 ` Herbert Xu [this message]
2018-09-07 6:20 ` Olof Johansson
2018-09-07 7:03 ` Eric Dumazet
2018-09-07 7:21 ` Eric Dumazet
2018-09-08 17:02 ` Olof Johansson
2018-09-09 18:38 ` Eric Dumazet
2018-09-18 9:37 ` [LKP] [net/sock] b99259a614: netperf.Throughput_Mbps -6.6% regression kernel test robot
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