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Subject[PATCH 6/8] printk: Start printing handover kthreads on demand
Date
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 <jack@suse.cz>
---
kernel/printk/printk.c | 64 +++++++++++++++++++++++++++++++++++++++-----------
1 file changed, 50 insertions(+), 14 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index cb7e06850eb5..8d981b2b5bb1 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -109,6 +109,10 @@ static long printk_handover_state;
* 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);
@@ -280,6 +284,12 @@ 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
@@ -288,7 +298,7 @@ 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");
@@ -2571,30 +2581,56 @@ static int printing_task(void *arg)
return 0;
}

-static int __init printk_late_init(void)
+static void printk_start_offload_kthreads(void)
{
- struct console *con;
int i;
struct task_struct *task;

- for_each_console(con) {
- if (!keep_bootcon && con->flags & CON_BOOT) {
- unregister_console(con);
- }
- }
- hotcpu_notifier(console_cpu_notify, 0);
-
- /* Does any handover of printing have any sence? */
- if (num_possible_cpus() <= 1)
- return 0;
-
+ /* Does handover of printing make any sense? */
+ if (printk_offload_chars == 0 || num_possible_cpus() <= 1)
+ return;
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)) {
pr_err("printk: Cannot create printing thread: %ld\n",
PTR_ERR(task));
}
+ printing_kthread[i] = 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;
+ }
+ printk_start_offload_kthreads();
+ mutex_unlock(&printk_kthread_mutex);
+ return 0;
+}
+
+static int __init printk_late_init(void)
+{
+ struct console *con;
+
+ for_each_console(con) {
+ if (!keep_bootcon && con->flags & CON_BOOT) {
+ unregister_console(con);
+ }
+ }
+ hotcpu_notifier(console_cpu_notify, 0);
+
+ mutex_lock(&printk_kthread_mutex);
+ printk_start_offload_kthreads();
+ mutex_unlock(&printk_kthread_mutex);

return 0;
}
--
1.8.1.4


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