linux-kernel - [PATCH] events: Improve the "perf samples too long" warning

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Message-Id: <f385628fe8fbab4af39f6fe36728ce0e3611b616.1394301632.git.luto@amacapital.net>
Date:	Sat,  8 Mar 2014 10:02:33 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	linux-kernel@...r.kernel.org
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Ingo Molnar <mingo@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Bolle <pebolle@...cali.nl>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Andy Lutomirski <luto@...capital.net>
Subject: [PATCH] events: Improve the "perf samples too long" warning

The warning is not indicative of an actual problem, especially when
triggered by nmi_watchdog, so lower it to KERN_INFO.  While I'm at
it, clarify the message and reference the sysctl that controls it.

Signed-off-by: Andy Lutomirski <luto@...capital.net>
---
 kernel/events/core.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 56003c6..245bdc0 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -263,9 +263,8 @@ void perf_sample_event_took(u64 sample_len_ns)
 	sysctl_perf_event_sample_rate = max_samples_per_tick * HZ;
 	perf_sample_period_ns = NSEC_PER_SEC / sysctl_perf_event_sample_rate;
 
-	printk_ratelimited(KERN_WARNING
-			"perf samples too long (%lld > %lld), lowering "
-			"kernel.perf_event_max_sample_rate to %d\n",
+	printk_ratelimited(KERN_INFO
+			"perf samples are too slow for kernel.perf_cpu_time_max_percent (%lldns > %lldns); lowering kernel.perf_event_max_sample_rate to %d\n",
 			avg_local_sample_len, allowed_ns,
 			sysctl_perf_event_sample_rate);
 
-- 
1.8.5.3

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