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@xxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxx> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
