[PATCH 00/17] coresight: next v4.12-rc4
From: Kim Phillips <hidden>
Date: 2017-06-15 14:22:46
On Thu, 15 Jun 2017 09:41:22 +0100 Sudeep Holla [off-list ref] wrote:
On 15/06/17 04:34, Kim Phillips wrote: [...]quoted
How does one tell whether writes to /dev/cpu_dma_latency are effective?Watch /sys/devices/system/cpu/cpu*/cpuidle/state*/{usage,time}, they shouldn't tick based on the value set to cpu_dma_latency. E.g. a value of 0 should stop entering all the idle states.
I see all states following the same pattern whether 0 or not:
root at juno:~# cat show2.sh
show()
{
echo $1 > /dev/cpu_dma_latency
echo === $1:
cat /sys/devices/system/cpu/cpu2/cpuidle/state*/{usage,time}
echo ---
sleep 10
cat /sys/devices/system/cpu/cpu2/cpuidle/state*/{usage,time}
}
show 0
show 1500
show 0
root at juno:~# taskset -c 2 bash ./show2.sh
=== 0:
1893
894
5417
1398675
65997648
3818880750
---
1895
905
5434
1401721
68076867
3826795502
=== 1500:
1895
905
5434
1401721
68076867
3826795502
---
1895
918
5447
1401721
69403510
3835466081
=== 0:
1895
918
5447
1401721
69403510
3835466081
---
1896
929
5463
1403577
71454839
3843409979
googling suggests the /dev/cpu_dma_latency file should be *kept* open,
and written a 32-bit binary number:
https://access.redhat.com/articles/65410
If so (I don't have time to test), this cpu debug documentation is very
deceptive.
Kim