Re: [PATCH 07/17] net: convert sock.sk_refcnt from atomic_t to refcount_t
From: Peter Zijlstra
Date: Mon Mar 20 2017 - 11:45:59 EST
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.