Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752304AbbGMMoA (ORCPT ); Mon, 13 Jul 2015 08:44:00 -0400 Received: from smtprelay.synopsys.com ([198.182.47.9]:50235 "EHLO smtprelay.synopsys.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752064AbbGMMn6 convert rfc822-to-8bit (ORCPT ); Mon, 13 Jul 2015 08:43:58 -0400 From: Vineet Gupta To: Peter Zijlstra CC: "linux-kernel@vger.kernel.org" , "linux-arch@vger.kernel.org" , "rth@twiddle.net" , "linux@arm.linux.org.uk" , "will.deacon@arm.com" , "hskinnemoen@gmail.com" , "realmz6@gmail.com" , "dhowells@redhat.com" , "rkuo@codeaurora.org" , "tony.luck@intel.com" , "geert@linux-m68k.org" , "james.hogan@imgtec.com" , "ralf@linux-mips.org" , "jejb@parisc-linux.org" , "benh@kernel.crashing.org" , "heiko.carstens@de.ibm.com" , "davem@davemloft.net" , "cmetcalf@ezchip.com" Subject: Re: [RFC][PATCH 02/24] arc: Provide atomic_{or,xor,and} Thread-Topic: [RFC][PATCH 02/24] arc: Provide atomic_{or,xor,and} Thread-Index: AQHQunCgyAH23JGzD0K9GR+krBLofg== Date: Mon, 13 Jul 2015 12:43:45 +0000 Message-ID: References: <20150709172855.564686637@infradead.org> <20150709175308.217482496@infradead.org> <20150710070511.GE19282@twins.programming.kicks-ass.net> Accept-Language: en-US, en-IN Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.12.197.226] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1900 Lines: 47 On Friday 10 July 2015 12:35 PM, Peter Zijlstra wrote: > On Fri, Jul 10, 2015 at 04:30:46AM +0000, Vineet Gupta wrote: >> > >> > Since we are on the topic, the cmpxchg() loop in arch/arc/kernel/smp.c still >> > irritates me. >> > Do we need a new set of primitives to operate atomically on non atomic_t data or >> > does that mean that the data *not* being atomic_t but requiring such semantics is >> > the fundamental problem and thus needs to be converted first. > So if you look at the last patch, there's already a few sites that do > things like: > > + atomic_or(*mask, (atomic_t *)&flushcache_cpumask); > > Which is of course ugly as hell, but does work. > > Esp. inside arch code. Right - I don't have issues with using this API - but this requires atomic_t data type. The specific cmpxchg() loop that I'm referring to is not for atomic_t - so that needs to be converted to atomic_t first ? > > Now the 'problem' with cmpxchg/xchg, the instructions working on !atomic > data is: > > http://lkml.kernel.org/r/alpine.LRH.2.02.1406011342470.20831@file01.intranet.prod.int.rdu2.redhat.com > http://lkml.kernel.org/r/20140606175316.GV13930@laptop.programming.kicks-ass.net > > And note that includes some arc. Correct so we don't mix cmpxchg() with normal load/store. > > Adding more such primitives will only make it harder on those already > 'broken' archs. Not sure if I follow here - my point was not so much about expanding the atomic_*() API but whether it makes sense to have "some" API for non atomic_t vs. converting the non atomic_t to atomic_t and then use the API as that is the fundamental problem for such cases. -Vineet -- 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/