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Fixed

LIN5-2715 : [WRL5.0.1] The preempt_rt kernel has a drop of the throughput and interrupt latency on the PPC boards, compared with 4.3.

Created: Dec 3, 2012    Updated: Dec 19, 2017
Resolved Date: Dec 31, 2013
Found In Version: 5.0.1
Fix Version: 5.0.1.11
Severity: Severe
Applicable for: Wind River Linux 5
Component/s: Kernel

Description

Problem Description
======================
1st issue: the preempt_rt kernel has a significant drop in the hackbench throughput on the PPC boards, rt kernel, compared with 4.3 kernel.

PPC board: p4080, e500mc bsp, rt kernel, glibc_std rootfs.

	10	20	30	40	50	60	70	80
Penguin 3.4.20-rt29 kernel + Penguin root fs	
1.9322 s  2.6724 s  4.11926666666667 s  5.2916 s  6.30844 s 	7.571 s 	  8.57537142857143 s 	9.535175 s 

ML 3.4.27 rt39 kernel + Penguin root fs	        
1.8646 s  2.6055 s   3.38786666666667 s  4.0438 s  4.6248 s  5.1229 s   5.71085714285714 s 	6.187475 s 

4.3 Kernel 2.6.34.10-rt + 4.3 root fs	                 
0.514 s	0.7382 s	   0.980533333333333 s	1.2147 s	         1.454 s	        1.7106 s	     1.95862857142857 s	2.208625 s

Penguin 3.4.20-rt29 kernel + 4.3  root fs	         
2.109 s	 3.3949 s    4.6518 s     6.0187 s	7.31332 s	8.2556 s	     9.58097142857143 s	10.3981 s

Current issue was the big drop on Penguin rt kernel, compared with 4.3 kernel.

2nd issue, I found that the Penguin rt kernel was worse than 4.3 kernel not only in the throughput (hackbench data), but also in the Real time performance "interrupt latency" (cyclictest data), the following data was under the same heavy load and sampled by 1,000,000 times.

(The smaller, the better)

Linux version 2.6.34.10-rt-WR4.3.0.0_preempt_rt
policy: fifo: loadavg: 309.05 247.54 148.15 37/271 4273
T: 0 (22322) P:99 I:1000 C:1000000 Min:      7 Act:   16 Avg:   15 Max:     110


Linux version 3.4.20-rt29-WR5.0.1.0_preempt-rt
policy: fifo: loadavg: 300.03 152.35 60.02 58/964 19135
T: 0 (27175) P:99 I:1000 C:1000000 Min:      7 Act:   19 Avg:   20 Max:     277

We can see the average value and the worst case value are all worse than wrlinux 4.3, in other words, the upgraded rt kernel have no improvement than before. 

Steps to Reproduce

1, config the project

/wrlinux/configure --enable-board=fsl-e500mc --enable-kernel=preempt-rt --enable-rootfs=glibc_std --with-layer=/buildarea1/hzhang/git/wr-testing/benchmark --template=feature/rt-benchmark --enable-jobs=10 --with-rcpl-version=auto

2, boot the kernel

/opt/benchmarks/rt-tests/run_test.pl

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