Re: [PATCH] net/sock: move memory_allocated over to percpu_counter variables

[Herbert Xu]

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>
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