From: Kunwu Chan <[email protected]> The original comments introduced in commit 05c5df31afd1 ("rcu: Make RCU able to tolerate undefined CONFIG_RCU_FANOUT"), contained confusing annotations.
Specifically, the #else and #endif comments did not clearly reflect their corresponding condition blocks, hampering readability. Fixes condition branch comments. And adds explicit explanations of the overall purpose: defining middle/leaf fan-out parameters, their relation to Kconfig, and how they shape the RCU hierarchy based on CPU count. Make the hierarchical configuration logic of the RCU easier to understand. Signed-off-by: Kunwu Chan <[email protected]> --- include/linux/rcu_node_tree.h | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/include/linux/rcu_node_tree.h b/include/linux/rcu_node_tree.h index 78feb8ba7358..b03c0ce91dec 100644 --- a/include/linux/rcu_node_tree.h +++ b/include/linux/rcu_node_tree.h @@ -25,26 +25,34 @@ /* * Define shape of hierarchy based on NR_CPUS, CONFIG_RCU_FANOUT, and * CONFIG_RCU_FANOUT_LEAF. + * - RCU_FANOUT: Controls fan-out of middle levels in the RCU hierarchy. + * - RCU_FANOUT_LEAF: Controls fan-out of the leaf level (directly managing CPUs). + * + * These parameters are determined by Kconfig options if configured; otherwise, + * they use sensible defaults based on system architecture (for RCU_FANOUT) + * or a fixed default (for RCU_FANOUT_LEAF). * In theory, it should be possible to add more levels straightforwardly. * In practice, this did work well going from three levels to four. * Of course, your mileage may vary. */ +/* Define RCU_FANOUT: middle-level fan-out parameter */ #ifdef CONFIG_RCU_FANOUT #define RCU_FANOUT CONFIG_RCU_FANOUT -#else /* #ifdef CONFIG_RCU_FANOUT */ +#else /* #ifndef CONFIG_RCU_FANOUT */ # ifdef CONFIG_64BIT # define RCU_FANOUT 64 # else # define RCU_FANOUT 32 # endif -#endif /* #else #ifdef CONFIG_RCU_FANOUT */ +#endif +/* Define RCU_FANOUT_LEAF: leaf-level fan-out parameter (manages CPUs directly) */ #ifdef CONFIG_RCU_FANOUT_LEAF #define RCU_FANOUT_LEAF CONFIG_RCU_FANOUT_LEAF -#else /* #ifdef CONFIG_RCU_FANOUT_LEAF */ +#else /* #ifndef CONFIG_RCU_FANOUT_LEAF */ #define RCU_FANOUT_LEAF 16 -#endif /* #else #ifdef CONFIG_RCU_FANOUT_LEAF */ +#endif #define RCU_FANOUT_1 (RCU_FANOUT_LEAF) #define RCU_FANOUT_2 (RCU_FANOUT_1 * RCU_FANOUT) -- 2.25.1
