On Thu, Sep 06, 2018 at 12:33:58PM -0700, Eric Dumazet wrote:

On Thu, Sep 6, 2018 at 12:21 PM Olof Johansson [off-list ref] wrote:

quoted

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 [off-list ref]
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