From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stanislav Meduna Subject: Bogus latency_hist/preemptirqsoff ? Date: Sat, 20 Apr 2013 13:46:17 +0200 Message-ID: <51728009.8030601@meduna.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit To: "linux-rt-users@vger.kernel.org" Return-path: Received: from www.meduna.org ([92.240.244.38]:45054 "EHLO meduna.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755068Ab3DTLq2 (ORCPT ); Sat, 20 Apr 2013 07:46:28 -0400 Received: from dial-95-105-165-4-orange.orange.sk ([95.105.165.4] helo=[192.168.130.22]) by meduna.org with esmtpsa (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.72) (envelope-from ) id 1UTWFJ-00009g-En for linux-rt-users@vger.kernel.org; Sat, 20 Apr 2013 13:46:23 +0200 Sender: linux-rt-users-owner@vger.kernel.org List-ID: Hi, what and how does the latency_hist/preemptirqsoff measure? The ftrace.txt says "preemptirqsoff" Similar to irqsoff and preemptoff, but traces and records the largest time for which irqs and/or preemption is disabled. # head -3 /sys/kernel/debug/tracing/latency_hist/wakeup/CPU0 #Minimum latency: 8 microseconds #Average latency: 15 microseconds #Maximum latency: 95 microseconds # head -3 /sys/kernel/debug/tracing/latency_hist/timerandwakeup/CPU0 #Minimum latency: 8 microseconds #Average latency: 15 microseconds #Maximum latency: 95 microseconds # head -3 /sys/kernel/debug/tracing/latency_hist/wakeup/sharedprio/CPU0 #Minimum latency: 9 microseconds #Average latency: 42 microseconds #Maximum latency: 603 microseconds (this is OK, there are such threads) # head -3 /sys/kernel/debug/tracing/latency_hist/irqsoff/CPU0 #Minimum latency: 0 microseconds #Average latency: 2 microseconds #Maximum latency: 136 microseconds # head -3 /sys/kernel/debug/tracing/latency_hist/preemptoff/CPU0 #Minimum latency: 2 microseconds #Average latency: 7 microseconds #Maximum latency: 121 microseconds # head -6 /sys/kernel/debug/tracing/latency_hist/preemptirqsoff/CPU0 #Minimum latency: 0 microseconds #Average latency: 2 microseconds #Maximum latency: 29001 microseconds #Total samples: 29054669 #There are 0 samples lower than 0 microseconds. #There are 15 samples greater or equal than 10240 microseconds. The 29 ms looks bogus. There are two test-applications running and each one would cry loudly being without CPU for 10 ms or more. Or is there a possibility that the irqsoff and preemptoff alternate so that everything looks normal but there is not a single time both are possible? 3.4.25-rt37, preempt full. Thanks -- Stano