Red Hat Bugzilla – Bug 244187
hald slows down system clock on systems with apm
Last modified: 2013-03-05 22:51:07 EST
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): hal-0.5.9-8.fc7 How reproducible: Always 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: http://www.ussg.iu.edu/hypermail/linux/kernel/0012.3/0669.html 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.
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We need /proc/apm for the battery and AC detection. It sounds like a kernel bug that needs fixing, not HAL. Sorry.