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

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Date:	Wed, 1 Apr 2015 15:59:10 -0400
From:	Len Brown <lenb@...nel.org>
To:	Adrian Hunter <adrian.hunter@...el.com>
Cc:	Ulf Hansson <ulf.hansson@...aro.org>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Kevin Hilman <khilman@...aro.org>,
	Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	Linux PM list <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/4] mmc: sdhci: Support maximum DMA latency request
 via PM QoS

> 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.

cheers,
Len Brown, Intel Open Source Technology Center
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