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Message-ID: <20110806225202.GO6058@hexapodia.org>
Date: Sat, 6 Aug 2011 15:52:02 -0700
From: Andy Isaacson <adi@...apodia.org>
To: linux-kernel@...r.kernel.org
Subject: powertop "pread cpu0 0xe8 : Bad file descriptor" fixed by
CONFIG_MSR
I hadn't seen this issue discussed on the list, and I don't know of a
powertop mailing list, so here's what stymied my use of powertop until I
straced it.
With CONFIG_MSR=n, powertop "1.97-2" (from Debian unstable) on 3.0.1
(and presumably many other recent kernels) exits at startup with:
pread cpu0 0xe8 : Bad file descriptor
strace shows:
open("/dev/cpu/0/msr", O_RDONLY) = -1 ENOENT (No such file or directory)
pread(4294967295, 0x7fff4c8347c8, 8, 232) = -1 EBADF (Bad file descriptor)
Setting CONFIG_MSR=m and loading msr.ko fixes the issue, allowing
powertop to work again (tested against 3.0.1). I'm pretty sure this is
a regression from long ago -- I have had CONFIG_X86_MSR=n in almost all
configs since 2.6.34-07097-gf4b87de, and powertop worked in most of
those kernels. But I don't have references for what versions of
powertop and what kernels I was running at various points.
-andy
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