[Bridge] [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to refcount_t

Peter Zijlstra peterz at infradead.org
Mon Mar 20 14:59:38 UTC 2017

On Mon, Mar 20, 2017 at 07:51:01AM -0700, Eric Dumazet wrote:
> PowerPC has no efficient atomic_inc() and this definitely shows on
> network intensive workloads involving concurrent cores/threads.

Correct, PPC LL/SC are dreadfully expensive.

> atomic_cmpxchg() on PowerPC is horribly more expensive because of the
> added two SYNC instructions.

Note that refcount_t uses atomic_cmpxchg_release() and
atomic_cmpxchg_relaxed() which avoid most of the painful barriers.

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