Messages in this thread | | | Subject | Re: [PATCH, RFC, tip/core/rcu] scalable classic RCU implementation | From | Josh Triplett <> | Date | Fri, 22 Aug 2008 11:16:38 -0700 |
| |
On Fri, 2008-08-22 at 10:22 -0700, Paul E. McKenney wrote: > 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 <paulmck@linux.vnet.ibm.com> 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.
Makes sense.
> So I took a hard look at the current mess, and prettied it as shown below. > Is this a sufficient improvement?
Looks significantly improved.
> Another alternative I am considering is moving this to a separate > include file.
I personally don't think that would help. The revised version seems fine.
> #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)
- Josh Triplett
| |