From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: [PATCH] atomic: add atomic_inc_not_zero_hint() Date: Fri, 05 Nov 2010 17:53:00 +0100 Message-ID: <1288975980.2882.877.camel@edumazet-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: linux-kernel , David Miller , netdev , Arnaldo Carvalho de Melo , Christoph Lameter , Ingo Molnar , Andi Kleen , "Paul E. McKenney" , Nick Piggin To: Andrew Morton Return-path: Received: from mail-wy0-f174.google.com ([74.125.82.174]:56910 "EHLO mail-wy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752788Ab0KEQxF (ORCPT ); Fri, 5 Nov 2010 12:53:05 -0400 Sender: netdev-owner@vger.kernel.org List-ID: Andrew atomic_inc_not_zero() / atomic_add_unless() ... are spreaded in many arch/xxx/include/asm/atomic.h, but they are generic. Apparently there is no centralization of some common atomic features... What do you think adding a new file so that we can move common definitions in it ? Thanks [PATCH] atomic: add atomic_inc_not_zero_hint() Followup of perf tools session in Netfilter WorkShop 2010 In network stack we make high usage of atomic_inc_not_zero() in contexts we know the probable value of atomic before increment (2 for udp sockets for example) Using a special version of atomic_inc_not_zero() giving this hint can help processor to use less bus transactions. On x86 (MESI protocol) for example, this avoids entering Shared state, because "lock cmpxchg" issues an RFO (Read For Ownership) Signed-off-by: Eric Dumazet Cc: Christoph Lameter Cc: Ingo Molnar Cc: Andi Kleen Cc: Arnaldo Carvalho de Melo Cc: David Miller Cc: "Paul E. McKenney" Cc: Nick Piggin --- include/linux/atomic.h | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) diff --git a/include/linux/atomic.h b/include/linux/atomic.h new file mode 100644 index 0000000..c04327a --- /dev/null +++ b/include/linux/atomic.h @@ -0,0 +1,29 @@ +#ifndef _LINUX_ATOMIC_H +#define _LINUX_ATOMIC_H +#include + +/** + * atomic_inc_not_zero_hint - increment if not null + * @v: pointer of type atomic_t + * @hint: probable value of the atomic before the increment + * + * This version of atomic_inc_not_zero() gives a hint of probable + * value of the atomic. This helps processor to not read the memory + * before doing the atomic read/modify/write cycle, lowering + * number of bus transactions on some arches. + * Note: hint MUST not be 0 ! + */ +static inline int atomic_inc_not_zero_hint(atomic_t *v, int hint) +{ + int val, c = hint; + + do { + val = atomic_cmpxchg(v, c, c + 1); + if (val == c) + return 1; + c = val; + } while (c); + + return 0; +} +#endif /* _LINUX_ATOMIC_H */