Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754007AbbGPVlt (ORCPT ); Thu, 16 Jul 2015 17:41:49 -0400 Received: from mga14.intel.com ([192.55.52.115]:19469 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751006AbbGPVlr (ORCPT ); Thu, 16 Jul 2015 17:41:47 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.15,490,1432623600"; d="scan'208";a="730357423" Message-ID: <1437082905.12633.56.camel@tzanussi-mobl.amr.corp.intel.com> Subject: Re: [PATCH v9 07/22] tracing: Add lock-free tracing_map From: Tom Zanussi To: Peter Zijlstra Cc: rostedt@goodmis.org, daniel.wagner@bmw-carit.de, masami.hiramatsu.pt@hitachi.com, namhyung@kernel.org, josh@joshtriplett.org, andi@firstfloor.org, linux-kernel@vger.kernel.org Date: Thu, 16 Jul 2015 16:41:45 -0500 In-Reply-To: <20150716174946.GH12596@twins.programming.kicks-ass.net> References: <777bd36975a1dd904fd6b72c4048474dd2327a65.1437066836.git.tom.zanussi@linux.intel.com> <20150716174946.GH12596@twins.programming.kicks-ass.net> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.10.4 (3.10.4-4.fc20) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1133 Lines: 29 On Thu, 2015-07-16 at 19:49 +0200, Peter Zijlstra wrote: > On Thu, Jul 16, 2015 at 12:22:40PM -0500, Tom Zanussi wrote: > > + for (i = 0; i < elt->map->n_fields; i++) { > > + atomic64_set(&dup_elt->fields[i].sum, > > + atomic64_read(&elt->fields[i].sum)); > > + dup_elt->fields[i].cmp_fn = elt->fields[i].cmp_fn; > > + } > > + > > + return dup_elt; > > +} > > So there is a lot of atomic64_{set,read}() in this patch set, what kind > of magic properties do you assume they have? > > Note that atomic*_{set,read}() are weaker than {WRITE,READ}_ONCE(), so > if you're assuming they do that, you're mistaken -- although it is on a > TODO list someplace to go fix that. Not assuming any magic properties - I just need an atomic 64-bit counter for the sums and that's the API for setting/reading those. When reading a live trace the exact sum you get is kind of arbitrary.. Tom -- 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/