I’ve had some problems with RTC on Dell PowerEdge servers with Debian 4.0 (etch), which were unfixable by all of the following:

  • Set Hz to 100/250/1000
  • Try newer kernel
  • Add –directisa option to hwclock (Would only fix a symptom of the problem, and not touch the problem itself at all)

The symptoms: You get a lot of messages like this: rtc: lost some interrupts at 2048Hz This varies (in my case) between 1024Hz, 2048Hz and 4096Hz. The message is printed to the terminal as fast as it can handle, and is written to syslog at a rate of 3500/sec – Though some times less. If you run “hwclock” on the system, it spits out an error message: select() to /dev/rtc to wait for clock tick timed out.

Chris Snyder suggests to avoid the problem instead of fixing it, by disabling precise timekeeping in VMware (Which is what was my main problem). What did fix the problem, however, was to compile a new kernel with HPET_EMULATE_RTC. This is more or less a battle in itself, as HPET_EMULATE_RTC depends on other stuff on its own. I’m to exhausted to give a proper walkthrough on this, as I’ve done about 50 kernel recompiles in the past week or so, and just want to forget this issue altogether ASAP.

Why HPET\_EMULATE\_RTC isn’t on by default is beyond my scope of comprehension, as there’s absolutely no good reason to not have it enabled unless you’re running an extremely small embedded kernel which doesn’t need it in the first place, in which case you’ll disabe it forcefully anyway.

Update: After notifying Chris about this blog post, he suggested that I update it with the kernel config options that I enabled to make HPET RTC emulation work. As opposed to what I wrote earlier, there’s not really hundreds of different .config options to edit. Only a few if you’re editing .config directly and only one if you’re using menuconf.

In menuconf, go Device Drivers ---> Character Devices ---> Enchanced Real Time Clock Support. You’ll see that it is built as a module. What we really need is to make it built-in. Just press Y. Now you can type / (slash) and search for HPET. Go to the bottom of the search results and you should hopefully see HPET\_EMULATE\_RTC=y. For all the others, here’s the diff for the Debian 2.6.18 kernel:


Please note, CONFIG\_HPET\_EMULATE\_RTC depends on CONFIG\_RTC=y.