From: Herbert Xu Subject: Re: [PATCH] net/sock: move memory_allocated over to percpu_counter variables Date: Fri, 7 Sep 2018 11:32:57 +0800 Message-ID: <20180907033257.2nlgiqm2t4jiwhzc@gondor.apana.org.au> References: <20180906192034.8467-1-olof@lixom.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Olof Johansson , David Miller , Neil Horman , Marcelo Ricardo Leitner , Vladislav Yasevich , Alexey Kuznetsov , Hideaki YOSHIFUJI , linux-crypto@vger.kernel.org, LKML , linux-sctp@vger.kernel.org, netdev , linux-decnet-user@lists.sourceforge.net, kernel-team To: Eric Dumazet Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-crypto.vger.kernel.org On Thu, Sep 06, 2018 at 12:33:58PM -0700, Eric Dumazet wrote: > On Thu, Sep 6, 2018 at 12:21 PM Olof Johansson 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 Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt