Hi John,
[..]
If running a half-decent version of cyclictest, sleep states are generally
disabled while cyclictest is running. Please watch the line
# /dev/cpu_dma_latency set to 0us
which essentially documents this mechanism. Yes, the name of the variable
"cpu_dma_latency" is not obvious and cyclictest could do a better job by
writing
Wrote 0 to /dev/cpu_dma_latency and keeping the path open to prevent
all cores from entering any sleep state
but this is another story.
Not sure what you mean here, doesn't it keep the path open?
No, no, cyclictest does the right thing and keeps the path open as
required. This is all good.
The message "/dev/cpu_dma_latency set to 0us" apparently is not clear
enough. It has nothing to do with DMA but the purpose of setting the
kernel variable cpu_dma_latency to 0 is to generally disable sleep
states. But I better should have submitted a patch.
-Carsten.
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