Bug 244187 - hald slows down system clock on systems with apm
hald slows down system clock on systems with apm
Product: Fedora
Classification: Fedora
Component: hal (Show other bugs)
All Linux
low Severity low
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Assigned To: David Zeuthen
Depends On:
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Reported: 2007-06-14 09:14 EDT by nvwarr
Modified: 2013-03-05 22:51 EST (History)
2 users (show)

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Fixed In Version:
Doc Type: Bug Fix
Doc Text:
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Clone Of:
Last Closed: 2008-05-30 07:30:57 EDT
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RHEL 7.3 requirements from Atomic Host:
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Description nvwarr 2007-06-14 09:14:37 EDT
Description of problem:
hald reads /proc/apm every 2 seconds, which causes the system clock to slow down.

Version-Release number of selected component (if applicable):

How reproducible:

Steps to Reproduce:
1. Stop hald.
2. System clock runs normally.
3. Restart hald.
4. System clock runs slow.
Actual results:
Hald slows down the system clock to such an extent and with such a large jitter
that ntp is no longer able to keep the system time synchronized, resulting in
massive clock drifts (i.e. hours). On my system, the slowdown was about 10 hours
per week.

Expected results:
Hald shouldn't slow down the system clock.

Additional info:
Actually, this is really a kernel bug, because any user can cat /proc/apm, which
has the same effect. I have filed a bug report against the kernel package too
(see https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=244177). However, this
is not a new bug in the kernel and when it was reported against kernel 2.2.18
over six years ago, the thread ended with Erik Mouw suggesting caching the
results of /proc/apm and Alan Cox saying this is a userspace issue:

In other words, unless the kernel people can fix the problem with /proc/apm,
userspace programs shouldn't read /proc/apm that frequently.

Commenting out lines 391 and 392 in hald/linux/apm.c (i.e. so read_from_apm is
no longer called) works around the problem.
Comment 1 Bug Zapper 2008-05-14 09:04:46 EDT
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Comment 2 Richard Hughes 2008-05-30 07:30:57 EDT
We need /proc/apm for the battery and AC detection. It sounds like a kernel bug
that needs fixing, not HAL. Sorry.

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