Hi, after some chatting with Nicholas and being sure that I didn't do anything totally stupid I would like to provide my current kernel config and a trace generated by "cyclictest ... -b500". kernel config -> https://www.dropbox.com/s/zsud0b77xoosjm1/config trace -> https://www.dropbox.com/s/5uf58oqo0qwcn4x/trace-cyclictest-2508us.txt I still get max latencies of about 4000us on this TI AM335x system running 3.12.6-rt9 with timers-do-not-raise-softirq-unconditionally.patch reverse applied. sched_rt_runtime_us and sched_rt_period_us are identical. The system is idle during the test. Rootfilesystem comes via NFS. root@generic-armv7a:~# cat /proc/sys/kernel/sched_rt_runtime_us 1000000 root@generic-armv7a:~# cat /proc/sys/kernel/sched_rt_period_us 1000000 root@generic-armv7a:~# uname -a Linux generic-armv7a 3.12.6-rt9-dirty #3 SMP PREEMPT RT Sat Jan 4 23:01:19 CET 2014 armv7l GNU/Linux root@generic-armv7a:~# ~/cyclictest -p99 -m -n -i200 -h400 -q -l100000 -b 500 # /dev/cpu_dma_latency set to 0us INFO: debugfs mountpoint: /sys/kernel/debug/tracing/ could not set ftrace_enabled to 0 could not set tracing_max_latency to 0 # Histogram ... # Total: 000018604 # Min Latencies: 00024 # Avg Latencies: 00158 # Max Latencies: 02508 # Histogram Overflows: 00212 # Histogram Overflow at cycle number: # Thread 0: ... ... # Thread Ids: 01126 # Break thread: 1126 # Break value: 2508 Does any of you have an idea where this big max. latency comes from? Matthias On 01/01/2014 05:37 PM, Matthias Fuchs wrote: > Hi, > > I did a setup with 3.12.6-rt9 kernel on a Beaglebone board > with an TI AM335x CPU running at fixed 720MHz. The kernel uses the > omap2plus_defconfig configuration that comes with this kernel with > additional CONFIG_PREEMPT_RT_FULL switched on. > > I am observing some strange max. latencies when comparing with kernel > 3.2.45-rt66. The results of a similiar system can be found on the OSADL lab > site (https://www.osadl.org/Latency-plot-of-system-in-rack-7-slot.qa-latencyplot-r7s5.0.html). > > With "cyclictest -p99 -m -n -i200 -h400 -q -l10000000" I get > ... > # Min Latencies: 00013 > # Avg Latencies: 00062 > # Max Latencies: 04664 > ... > > Also the latency does not differ much from that when doing a flood ping against > the system as simple stress. > > 3.2.45-rt66 comes with a max. latency of 118us! So I expect something to be wrong with 3.12.6-rt9 > at least on armv7 or especially this device (max. lat. 4664us). > > I also noticed an issue with the on-chip ethernet when CONFIG_PREEMPT_RT_FULL is > switched on with this kernel: > > I also noticed that the 3.12.6-rt9 with enabled > [ 2.817024] net eth0: initializing cpsw version 1.12 (0) > [ 2.825269] net eth0: phy found : id is : 0x7c0f1 > [ 2.830713] libphy: PHY 4a101000.mdio:01 not found > [ 2.835777] net eth0: phy 4a101000.mdio:01 not found on slave 1 > [ 12.846394] Waiting up to 110 more seconds for network. > [ 22.846147] Waiting up to 100 more seconds for network. > ... > > Finally networking is fine. But I need to wait for 110 seconds :-) > > Prior testing with 3.12.6-rt9 I did the same test with 3.12.5-rt7. Same results. > But without CONFIG_PREEMPT_RT_FULL I do not get this bringup delay. I could not do this > test with rt9 because it does not build without CONFIG_PREEMPT_RT_FULL! > > Any ideas? > > Matthias > -- > To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
