Re: [RFC PATCH 0/4] mmc: sdhci: Support maximum DMA latency request via PM QoS

From: Adrian Hunter
Date: Thu Apr 02 2015 - 15:35:29 EST

On 1/04/2015 10:59 p.m., Len Brown wrote:
Ad hoc testing with Lenovo Thinkpad 10 showed a stress
test could run for at least 24 hours with the patches,
compared to less than an hour without.

There is a patch in linux-next to delete C1E from BYT,
since it is problematic on multiple platforms.
I don't suppose that just disabling that state without disabling C6
is sufficient to fix the Thinkpad 10? (I'm betting not, but
it can't hurt to try -- you can use the "disable" attribute for the state
in /sys/devices/system/cpu/cpu*/cpuidle/stateN)

I think your choice of the PM_QOS sub-system here is the right one,
and that your selection of 20usec threshold is also a good choice
for what you want to do -- though on non-intel_idle machine somplace,
there may be some ACPI BIOS _CST with random number for C6 latency.

It would be interesting to see how your C6 residency (turbostat
--debug will show this to you)
and your battery life are changed by disabling C6 during MMC activity.

I will do some more testing as you suggest, although it will have to
wait until next week due to Easter holidays here.
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