linux-kernel - [RFC][PATCHv6 03/12] printk: consider watchdogs thresholds for offloading

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Date:   Mon,  4 Dec 2017 22:48:16 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Petr Mladek <pmladek@...e.com>
Cc:     Jan Kara <jack@...e.cz>, Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Pavel Machek <pavel@....cz>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: [RFC][PATCHv6 03/12] printk: consider watchdogs thresholds for offloading

There are several watchdogs, using different timeout values, so
we need to set printk offloading threshold appropriately. This
patch set extends offloading_threshold() to take RCU, softlockup
and hardlockup timeouts into consideration.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
---
 kernel/printk/printk.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index f4e84f83bff5..3d4df3f02854 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -492,10 +492,29 @@ void printk_emergency_end(void)
 }
 EXPORT_SYMBOL_GPL(printk_emergency_end);
 
+/*
+ * Adjust max timeout value in the following order:
+ * a) 1/2 of RCU stall timeout - it is usually the largest
+ * b) 1/2 of hardlockup threshold (if enabled) - lower than softlockup
+ * c) 1/2 of softlockup threshold (if enabled)
+ * e) default value - 10 seconds
+ */
 static inline int offloading_threshold(void)
 {
+	int timeout = CONFIG_RCU_CPU_STALL_TIMEOUT / 2 + 1;
+
+#ifdef CONFIG_LOCKUP_DETECTOR
+	/* Hardlockup detector has a sample_period of `watchdog_thresh'. */
+	if ((watchdog_enabled & NMI_WATCHDOG_ENABLED) && watchdog_thresh)
+		return min(timeout, watchdog_thresh / 2) + 1;
+
+	/* Softlockup uses '2 * watchdog_thresh' as a threshold value. */
+	if ((watchdog_enabled & SOFT_WATCHDOG_ENABLED) && watchdog_thresh)
+		return min(timeout, watchdog_thresh) + 1;
+#endif
+
 	/* Default threshold value is 10 seconds */
-	return 10;
+	return min(10, timeout);
 }
 
 /*
-- 
2.15.1