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Date: Fri, 11 Dec 2015 00:10:25 +0900
From: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To: Jan Kara <jack@...e.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Petr Mladek <pmladek@...e.cz>,
KY Srinivasan <kys@...rosoft.com>,
Steven Rostedt <rostedt@...dmis.org>,
linux-kernel@...r.kernel.org,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: Re: [PATCH 5/7] printk: Add config option for disabling printk
offloading
> Necessity for offloading of printing was observed only for large
> systems. So add a config option (disabled by default) which removes most
> of the overhead added by this functionality.
to be folded:
- add spin_lock_init_print_lock() to be called from zap_lock()
- move PRINTK_OFFLOAD defines up, so zap_lock() sees them
---
kernel/printk/printk.c | 119 ++++++++++++++++++++++++++-----------------------
1 file changed, 63 insertions(+), 56 deletions(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 2a500a5..86f5abf 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -333,7 +333,66 @@ 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");
-#endif
+
+/*
+ * Returns true iff there is other cpu waiting to take over printing. This
+ * function also takes are of setting PRINTK_HANDOVER_B if we want to hand over
+ * printing to some other cpu.
+ */
+static bool cpu_stop_printing(int printed_chars)
+{
+ /* Oops? Print everything now to maximize chances user will see it */
+ if (oops_in_progress)
+ return false;
+ if (!printk_offload_chars || printed_chars < printk_offload_chars)
+ return false;
+ /*
+ * Make sure we load fresh value of printing_tasks_spinning. Matches
+ * the barrier in printing_task()
+ */
+ smp_rmb();
+ if (atomic_read(&printing_tasks_spinning))
+ return true;
+ wake_up(&print_queue);
+
+ return false;
+}
+
+static bool cpu_should_cond_resched(bool do_cond_resched)
+{
+ /* Oops? Print everything now to maximize chances user will see it */
+ if (oops_in_progress)
+ return false;
+ if (!printk_offload_chars && do_cond_resched)
+ return true;
+ return false;
+}
+
+#define spin_lock_print_lock(flags) raw_spin_lock_irqsave(&print_lock, flags)
+
+#define spin_unlock_print_lock(flags) raw_spin_unlock_irqrestore(&print_lock, flags)
+
+#define spin_lock_init_print_lock() raw_spin_lock_init(&print_lock)
+
+#else /* !CONFIG_PRINTK_OFFLOAD */
+
+static bool cpu_stop_printing(int printed_chars)
+{
+ return false;
+}
+
+static bool cpu_should_cond_resched(bool do_cond_resched)
+{
+ return do_cond_resched && !oops_in_progress;
+}
+
+#define spin_lock_print_lock(flags) local_irq_save(flags)
+
+#define spin_unlock_print_lock(flags) local_irq_restore(flags)
+
+#define spin_lock_init_print_lock()
+
+#endif /* CONFIG_PRINTK_OFFLOAD */
/* Return log buffer address */
char *log_buf_addr_get(void)
@@ -1531,7 +1590,7 @@ static void zap_locks(void)
/* If a crash is occurring, make sure we can't deadlock */
raw_spin_lock_init(&logbuf_lock);
/* And make sure that we print immediately */
- raw_spin_lock_init(&print_lock);
+ spin_lock_init_print_lock();
sema_init(&console_sem, 1);
}
@@ -2265,58 +2324,6 @@ out:
raw_spin_unlock_irqrestore(&logbuf_lock, flags);
}
-#ifdef CONFIG_PRINTK_OFFLOAD
-/*
- * Returns true iff there is other cpu waiting to take over printing. This
- * function also takes are of setting PRINTK_HANDOVER_B if we want to hand over
- * printing to some other cpu.
- */
-static bool cpu_stop_printing(int printed_chars)
-{
- /* Oops? Print everything now to maximize chances user will see it */
- if (oops_in_progress)
- return false;
- if (!printk_offload_chars || printed_chars < printk_offload_chars)
- return false;
- /*
- * Make sure we load fresh value of printing_tasks_spinning. Matches
- * the barrier in printing_task()
- */
- smp_rmb();
- if (atomic_read(&printing_tasks_spinning))
- return true;
- wake_up(&print_queue);
-
- return false;
-}
-
-static bool cpu_should_cond_resched(bool do_cond_resched)
-{
- /* Oops? Print everything now to maximize chances user will see it */
- if (oops_in_progress)
- return false;
- if (!printk_offload_chars && do_cond_resched)
- return true;
- return false;
-}
-
-#define spin_lock_print_lock(flags) raw_spin_lock_irqsave(&print_lock, flags)
-
-#define spin_unlock_print_lock(flags) raw_spin_unlock_irqrestore(&print_lock, flags)
-
-#else
-
-static bool cpu_stop_printing(int printed_chars)
-{
- return false;
-}
-
-#define spin_lock_print_lock(flags) local_irq_save(flags)
-
-#define spin_unlock_print_lock(flags) local_irq_restore(flags)
-
-#endif
-
/**
* console_unlock - unlock the console system
*
@@ -2440,9 +2447,9 @@ skip:
printed_chars += len;
if (unlikely(cpu_should_cond_resched(do_cond_resched))) {
- raw_spin_unlock_irqrestore(&print_lock, flags);
+ spin_unlock_print_lock(flags);
cond_resched();
- raw_spin_lock_irqsave(&print_lock, flags);
+ spin_lock_print_lock(flags);
}
}
--
2.6.3
--
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