Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751688AbbGIIOA (ORCPT ); Thu, 9 Jul 2015 04:14:00 -0400 Received: from us01smtprelay-2.synopsys.com ([198.182.47.9]:33324 "EHLO smtprelay.synopsys.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750843AbbGIINr (ORCPT ); Thu, 9 Jul 2015 04:13:47 -0400 From: Vineet Gupta To: Peter Zijlstra , Ingo Molnar , Arnd Bergmann CC: , , Vineet Gupta Subject: [PATCH 0/3] atomic_or() related changes Date: Thu, 9 Jul 2015 13:43:16 +0530 Message-ID: <1436429599-10762-1-git-send-email-vgupta@synopsys.com> X-Mailer: git-send-email 1.9.1 MIME-Version: 1.0 Content-Type: text/plain X-Originating-IP: [10.12.197.226] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1995 Lines: 61 Hi, This started off as an effort to convert a cmpxchg based loop in arc/kernel/smp.c to an API which is more LLOCK/SCOND friendly. e.g. do { new = old = ACCESS_ONCE(*ipi_data_ptr); new |= 1U << msg; } while (cmpxchg(ipi_data_ptr, old, new) != old); The generated code is horrible. There are 2 useless branches here and a LD/LLOCK to same address all inside a loop. 8015cefc: ld_s r2,[r3,0] 8015cefe: or r5,r2,r1 8015cf02: llock r4,[r3] 8015cf06: brne r4,r2,8015cf12 8015cf0a: scond r5,[r3] 8015cf0e: bnz 8015cf02 8015cf12: brne r2,r4,8015cefc An atomic_or() kind of API is better suited to generate something like below 8015cf02: llock r4,[r3] 8015cf06: or r5,r2,r1 8015cf0a: scond r5,[r3] 8015cf0e: bnz 8015cf02 Although this doesn't work for the specific instance I wanted to fix as ipi_data_ptr is not atomic_t, I did run into a few things which could be improved, hence this series. Compile tested on ARC, ARM, x86. I do have some concern about mixing long and int on 64 bit arch, which I've captured inline in patch 2/3. It is most likely a lack of understand on my part, but worth asking.. Thx, -Vineet Vineet Gupta (3): asm-generic/atomic.h: ARCH_HAS_ATOMIC_OR -> CONFIG_ARCH_HAS_ATOMIC_OR brcmfmac: dhd_sdio.c: use existing atomic_or primitive ARC: provide atomic_or() and define ARCH_HAS_ATOMIC_OR arch/arc/include/asm/atomic.h | 9 +++++++++ drivers/net/wireless/brcm80211/brcmfmac/sdio.c | 13 ++----------- include/asm-generic/atomic.h | 2 +- include/linux/atomic.h | 4 ++-- 4 files changed, 14 insertions(+), 14 deletions(-) -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/