From: Jan Kara <[email protected]> Start kthreads for handing over printing only when printk.offload_chars is set to value > 0 (i.e., when print offloading gets enabled).
Signed-off-by: Jan Kara <[email protected]> --- kernel/printk/printk.c | 78 +++++++++++++++++++++++++++++++++++++++++--------- 1 file changed, 64 insertions(+), 14 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 1b26263edfa7..b9bb4a7a6dff 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -98,6 +98,10 @@ static atomic_t printing_tasks_spinning = ATOMIC_INIT(0); * CPUs. */ #define PRINTING_TASKS 2 +/* Pointers to printing kthreads */ +static struct task_struct *printing_kthread[PRINTING_TASKS]; +/* Serialization of changes to printk_offload_chars and kthread creation */ +static DEFINE_MUTEX(printk_kthread_mutex); /* Wait queue printing kthreads sleep on when idle */ static DECLARE_WAIT_QUEUE_HEAD(print_queue); @@ -303,6 +307,13 @@ static u32 clear_idx; static char __log_buf[__LOG_BUF_LEN] __aligned(LOG_ALIGN); static char *log_buf = __log_buf; static u32 log_buf_len = __LOG_BUF_LEN; + +static int offload_chars_set(const char *val, const struct kernel_param *kp); +static struct kernel_param_ops offload_chars_ops = { + .set = offload_chars_set, + .get = param_get_uint, +}; + /* * How many characters can we print in one call of printk before asking * other cpus to continue printing. 0 means infinity. Tunable via @@ -311,7 +322,7 @@ static u32 log_buf_len = __LOG_BUF_LEN; */ static unsigned int __read_mostly printk_offload_chars = 1000; -module_param_named(offload_chars, printk_offload_chars, uint, +module_param_cb(offload_chars, &offload_chars_ops, &printk_offload_chars, S_IRUGO | S_IWUSR); MODULE_PARM_DESC(offload_chars, "offload printing to console to a different" " cpu after this number of characters"); @@ -2778,12 +2789,61 @@ static int printing_task(void *arg) return 0; } -static int __init printk_late_init(void) +static int printk_start_offload_kthreads(void) { - struct console *con; int i; struct task_struct *task; + /* Does handover of printing make any sense? */ + if (printk_offload_chars == 0 || num_possible_cpus() <= 1) + return 0; + for (i = 0; i < PRINTING_TASKS; i++) { + if (printing_kthread[i]) + continue; + task = kthread_run(printing_task, NULL, "print/%d", i); + if (IS_ERR(task)) + goto out_err; + printing_kthread[i] = task; + } + return 0; +out_err: + pr_err("printk: Cannot create printing thread: %ld\n", PTR_ERR(task)); + /* Disable offloading if creating kthreads failed */ + printk_offload_chars = 0; + return PTR_ERR(task); +} + +static int offload_chars_set(const char *val, const struct kernel_param *kp) +{ + int ret; + + /* Protect against parallel change of printk_offload_chars */ + mutex_lock(&printk_kthread_mutex); + ret = param_set_uint(val, kp); + if (ret) { + mutex_unlock(&printk_kthread_mutex); + return ret; + } + ret = printk_start_offload_kthreads(); + mutex_unlock(&printk_kthread_mutex); + return ret; +} + +static void printk_offload_init(void) +{ + mutex_lock(&printk_kthread_mutex); + if (num_possible_cpus() <= 1) { + /* Offloading doesn't make sense. Disable print offloading. */ + printk_offload_chars = 0; + } else + printk_start_offload_kthreads(); + mutex_unlock(&printk_kthread_mutex); +} + +static int __init printk_late_init(void) +{ + struct console *con; + for_each_console(con) { if (!keep_bootcon && con->flags & CON_BOOT) { unregister_console(con); @@ -2791,17 +2851,7 @@ static int __init printk_late_init(void) } hotcpu_notifier(console_cpu_notify, 0); - /* Does any handover of printing have any sence? */ - if (num_possible_cpus() <= 1) - return 0; - - for (i = 0; i < PRINTING_TASKS; i++) { - task = kthread_run(printing_task, NULL, "print/%d", i); - if (IS_ERR(task)) { - pr_err("printk: Cannot create printing thread: %ld\n", - PTR_ERR(task)); - } - } + printk_offload_init(); return 0; } -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
