Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755930AbYHVRWl (ORCPT ); Fri, 22 Aug 2008 13:22:41 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752396AbYHVRWb (ORCPT ); Fri, 22 Aug 2008 13:22:31 -0400 Received: from e34.co.us.ibm.com ([32.97.110.152]:52336 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751593AbYHVRWa (ORCPT ); Fri, 22 Aug 2008 13:22:30 -0400 Date: Fri, 22 Aug 2008 10:22:21 -0700 From: "Paul E. McKenney" To: Ingo Molnar Cc: linux-kernel@vger.kernel.org, cl@linux-foundation.org, akpm@linux-foundation.org, manfred@colorfullife.com, dipankar@in.ibm.com, josht@linux.vnet.ibm.com, schamp@sgi.com, niv@us.ibm.com, dvhltc@us.ibm.com, ego@in.ibm.com, laijs@cn.fujitsu.com, rostedt@goodmis.org Subject: Re: [PATCH, RFC, tip/core/rcu] scalable classic RCU implementation Message-ID: <20080822172221.GA9593@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20080821234318.GA1754@linux.vnet.ibm.com> <20080822043715.GD15212@elte.hu> <20080822134720.GG6875@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080822134720.GG6875@linux.vnet.ibm.com> User-Agent: Mutt/1.5.15+20070412 (2007-04-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4025 Lines: 105 On Fri, Aug 22, 2008 at 06:47:20AM -0700, Paul E. McKenney wrote: > On Fri, Aug 22, 2008 at 06:37:15AM +0200, Ingo Molnar wrote: > > > > * Paul E. McKenney wrote: > > > > > +#define MAX_RCU_LEVELS 3 > > > +#if NR_CPUS <= CONFIG_RCU_FANOUT > > > +#define NUM_RCU_LEVELS 1 > > > +#define NUM_RCU_LEVEL_1 1 > > > +#define NUM_RCU_LEVEL_2 NR_CPUS > > > +#define NUM_RCU_LEVEL_3 0 > > > +#define NUM_RCU_LEVEL_4 0 > > > +#define NUM_RCU_NODES NUM_RCU_LEVEL_1 > > > +#elif NR_CPUS <= CONFIG_RCU_FANOUT * CONFIG_RCU_FANOUT > > > +#define NUM_RCU_LEVELS 2 > > > +#define NUM_RCU_LEVEL_1 1 > > > +#define NUM_RCU_LEVEL_2 \ > > > + (((NR_CPUS) + (CONFIG_RCU_FANOUT) - 1) / (CONFIG_RCU_FANOUT)) > > > +#define NUM_RCU_LEVEL_3 NR_CPUS > > > +#define NUM_RCU_LEVEL_4 0 > > > +#define NUM_RCU_NODES \ > > > + ((NUM_RCU_LEVEL_1) + (NUM_RCU_LEVEL_2)) > > > +#elif NR_CPUS <= CONFIG_RCU_FANOUT * CONFIG_RCU_FANOUT * CONFIG_RCU_FANOUT > > > +#define NUM_RCU_LEVELS 3 > > > +#define RCU_FANOUT_SQ ((CONFIG_RCU_FANOUT) * (CONFIG_RCU_FANOUT)) > > > +#define NUM_RCU_LEVEL_1 1 > > > +#define NUM_RCU_LEVEL_2 \ > > > + (((NR_CPUS) + (RCU_FANOUT_SQ) - 1) / (RCU_FANOUT_SQ)) > > > +#define NUM_RCU_LEVEL_3 \ > > > + ((NR_CPUS) + (CONFIG_RCU_FANOUT) - 1) / (CONFIG_RCU_FANOUT) > > > +#define NUM_RCU_LEVEL_4 NR_CPUS > > > +#define NUM_RCU_NODES \ > > > + ((NUM_RCU_LEVEL_1) + \ > > > + (NUM_RCU_LEVEL_2) + \ > > > + (NUM_RCU_LEVEL_3)) > > > +#else > > > +#error "CONFIG_RCU_FANOUT insufficient for NR_CPUS" > > > +#endif > > > > just a quick stylistic suggestion: if feasible then such sizing ugliness > > should be hidden in a Kconfig file. (if Kconfig is capable enough for > > this that is) > > I have no idea if Kconfig can do it, but I will check. OK, Kconfig does not currently support arithmetic, based on zconf.y: expr: symbol { $$ = expr_alloc_symbol($1); } | symbol T_EQUAL symbol { $$ = expr_alloc_comp(E_EQUAL, $1, $3); } | symbol T_UNEQUAL symbol { $$ = expr_alloc_comp(E_UNEQUAL, $1, $3); } | T_OPEN_PAREN expr T_CLOSE_PAREN { $$ = $2; } | T_NOT expr { $$ = expr_alloc_one(E_NOT, $2); } | expr T_OR expr { $$ = expr_alloc_two(E_OR, $1, $3); } | expr T_AND expr { $$ = expr_alloc_two(E_AND, $1, $3); } ; All we currently get is basic comparison and logical operators. It would not be all -that- hard to add general arithmetic (famous last words), but when I tried mapping out what the sizing code would look like in such an augmented Kconfig, it was even uglier than the above. So I took a hard look at the current mess, and prettied it as shown below. Is this a sufficient improvement? Another alternative I am considering is moving this to a separate include file. Thoughts? Thanx, Paul #define MAX_RCU_LEVELS 3 #define RCU_FANOUT (CONFIG_RCU_FANOUT) #define RCU_FANOUT_SQ (RCU_FANOUT * RCU_FANOUT) #define RCU_FANOUT_CUBE (RCU_FANOUT_SQ * RCU_FANOUT) #if (NR_CPUS) <= RCU_FANOUT # define NUM_RCU_LVLS 1 # define NUM_RCU_LVL_0 1 # define NUM_RCU_LVL_1 (NR_CPUS) # define NUM_RCU_LVL_2 0 # define NUM_RCU_LVL_3 0 #elif (NR_CPUS) <= RCU_FANOUT_SQ # define NUM_RCU_LVLS 2 # define NUM_RCU_LVL_0 1 # define NUM_RCU_LVL_1 (((NR_CPUS) + RCU_FANOUT - 1) / RCU_FANOUT) # define NUM_RCU_LVL_2 (NR_CPUS) # define NUM_RCU_LVL_3 0 #elif (NR_CPUS) <= RCU_FANOUT_CUBE # define NUM_RCU_LVLS 3 # define NUM_RCU_LVL_0 1 # define NUM_RCU_LVL_1 (((NR_CPUS) + RCU_FANOUT_SQ - 1) / RCU_FANOUT_SQ) # define NUM_RCU_LVL_2 (((NR_CPUS) + (RCU_FANOUT) - 1) / (RCU_FANOUT)) # define NUM_RCU_LVL_3 NR_CPUS #else # error "CONFIG_RCU_FANOUT insufficient for NR_CPUS" #endif /* #if (NR_CPUS) <= RCU_FANOUT */ #define RCU_SUM (NUM_RCU_LVL_0 + NUM_RCU_LVL_1 + NUM_RCU_LVL_2 + NUM_RCU_LVL_3) #define NUM_RCU_NODES (RCU_SUM - NR_CPUS) -- 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/