linux-kernel - Re: /sys/module/pcie_aspm/parameters/policy not writable?

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Date:	Tue, 9 Jul 2013 11:49:06 +0200
From:	Pavel Machek <pavel@....cz>
To:	Greg KH <greg@...ah.com>
Cc:	kernel list <linux-kernel@...r.kernel.org>,
	joe.lawrence@...atus.com, myron.stowe@...hat.com,
	bhelgaas@...gle.com
Subject: Re: /sys/module/pcie_aspm/parameters/policy not writable?

On Mon 2013-07-08 21:13:21, Greg KH wrote:
> On Tue, Jul 09, 2013 at 03:26:11AM +0200, Pavel Machek wrote:
> > Hi!
> > 
> > My thinkpad has rather high ping latencies... and perhaps it is due to
> > PCIE ASPM.
> 
> Why would that be the problem?  The odds that the PCIE bus is the issue
> seems strange to me.

Aha: I guess that's why the file is not writable:

pavel@amd:~$ dmesg | grep -i aspm 
ACPI FADT declares the system doesn't support PCIe ASPM, so disable it
e1000e 0000:02:00.0: Disabling ASPM L0s L1
pavel@amd:~$ cat /sys/module/pcie_aspm/parameters/policy
[default] performance powersave 
pavel@amd:~$ 
root@amd:~# echo -n performance >
/sys/module/pcie_aspm/parameters/policy
-su: echo: write error: Operation not permitted
root@amd:~# 

But:
1) it should not list unavailable options

2) operation not permitted seems like wrong error code for
operation not supported.

									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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