From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthias Meier Subject: Re: Long max latencies on Wandbaord / Freescale i.MX6 Date: Tue, 29 Sep 2015 08:30:56 +0200 Message-ID: <560A3020.5090909@gmx.net> References: <5606677A.1020705@gmx.net> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit To: linux-rt-users@vger.kernel.org Return-path: Received: from mout.gmx.net ([212.227.17.22]:51648 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753740AbbI2Ga7 (ORCPT ); Tue, 29 Sep 2015 02:30:59 -0400 Received: from localhost.localdomain ([213.188.224.136]) by mail.gmx.com (mrgmx101) with ESMTPSA (Nemesis) id 0Lbi2Z-1aMRyc0TsZ-00lCz0 for ; Tue, 29 Sep 2015 08:30:57 +0200 In-Reply-To: Sender: linux-rt-users-owner@vger.kernel.org List-ID: just for imformation what causes the long latencies... cause of the latency problem of up to 10ms was 'CONFIG_PROVE_LOCKING' enabled in the kernel config. After disabling it, the max latency is now below 400us. (many thx to tglx who found the problem). The following arm boards have 'CONFIG_PROVE_LOCKING=y' in the defconfig and therefore the same problem: ezx_defconfig imote2_defconfig imx_v6_v7_defconfig moxart_defconfig mxs_defconfig omap2plus_defconfig Regards Matthias Am 27.09.2015 um 13:49 schrieb Thomas Gleixner: > On Sat, 26 Sep 2015, Matthias Meier wrote: > >> Hi, >> >> using cyclictest I measure long max latencies of >10ms on a Wandboard dual >> (Freescale i.MX6 dual Cortex-A9 SoC). >> >> The latency problem happens with diffent scenarios: >> - without or with rt-patch (4.1.7-rt8 w. CONFIG_PREEMPT_RT_FULL) >> - different Kernels (3.17, 4.1, 4.2 w. CONFIG_PREEMPT__LL) >> - different CPU governors including 'performance' >> - independant of CPU load >> - even with no other userspace processes but init, the login sh and cyclictest >> (I use a minimal builroot rfs). >> - independant of cyclictest prio >> >> Using the same buildroot rfs on a A20 SoC (bananapro) with 4.1.7-rt8 shows >> acceptable rt-latencies of ~ 200us. >> >> Ftracing 'irqsoff' on the rt-patched 4.1 kernel shows always long latency >> after 'raw_spin_lock_irq' (see log below). >> >> Do you think it is a driver which stalls or hrtimer not working correctly on >> this SoC or someting else? >> If it is a driver, how could I find out which it is? > > Try to capture the issue with full function tracing. > > cyclictest --smp -p80 -m -f -b 5000 > > That stops the tracer when the latency is > 5ms. You might have to > increase the trace buffer size. Please upload the trace to some place > or send it to me privately (it's over the size limit of the list). > > Thanks, > > tglx > >