Re: [patch 3/4] net: Percpufy frequently used variables -- proto.sockets_allocated

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Ravikiran G Thirumalai a écrit :
Change the atomic_t sockets_allocated member of struct proto to a per-cpu counter.

Signed-off-by: Pravin B. Shelar <[email protected]>
Signed-off-by: Ravikiran Thirumalai <[email protected]>
Signed-off-by: Shai Fultheim <[email protected]>

Hi Ravikiran

If I correctly read this patch, I think there is a scalability problem.

On a big SMP machine, read_sockets_allocated() is going to be a real killer.

Say we have 128 Opterons CPUS in a box.

You'll need to bring 128 cache lines (plus 8*128 bytes to read the 128 pointers inside percpu structure)

I think a solution 'a la percpu_counter' is preferable, or even better a dedicated per_cpu with a threshold management (see mm/swap.c , function vm_acct_memory() to see how vm_committed_space is updated without too bad SMP scalability)

Thank you

Eric

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