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Date: Fri, 10 Jul 2015 09:05:11 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Vineet Gupta <Vineet.Gupta1@...opsys.com> Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>, "rth@...ddle.net" <rth@...ddle.net>, "linux@....linux.org.uk" <linux@....linux.org.uk>, "will.deacon@....com" <will.deacon@....com>, "hskinnemoen@...il.com" <hskinnemoen@...il.com>, "realmz6@...il.com" <realmz6@...il.com>, "dhowells@...hat.com" <dhowells@...hat.com>, "rkuo@...eaurora.org" <rkuo@...eaurora.org>, "tony.luck@...el.com" <tony.luck@...el.com>, "geert@...ux-m68k.org" <geert@...ux-m68k.org>, "james.hogan@...tec.com" <james.hogan@...tec.com>, "ralf@...ux-mips.org" <ralf@...ux-mips.org>, "jejb@...isc-linux.org" <jejb@...isc-linux.org>, "benh@...nel.crashing.org" <benh@...nel.crashing.org>, "heiko.carstens@...ibm.com" <heiko.carstens@...ibm.com>, "davem@...emloft.net" <davem@...emloft.net>, "cmetcalf@...hip.com" <cmetcalf@...hip.com>, "mingo@...nel.org" <mingo@...nel.org> Subject: Re: [RFC][PATCH 02/24] arc: Provide atomic_{or,xor,and} 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. 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. Adding more such primitives will only make it harder on those already 'broken' archs. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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