Messages in this thread | | | Date | Sun, 14 Jun 1998 22:50:07 -0600 (MDT) | From | Colin Plumb <> | Subject | /dev/tsc and timekeeping |
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Included here is a small patch to add an interesting interrupt-latency measuring hack to the kernel. It's not ready for prime time, but might be fun to play with.
It's for x86 processors with a timestamp counter, and simply captures the the TSC on every clock interrupt and puts it in a circular buffer. Readers can read arbitrary amounts from it. Hopefully I implemented poll() correctly. The data you read starts from the moment you open() the device.
One thing I did was I put readers wanting a lot of data on a separate wait queue that gets woken up less frequently. This lets you see APM effects.
(One thing I'm wondering about APM is if it's worth calling apm_do_busy so early, or if we should wait until we've had a jiffy or two with no idle time, meaning that we need more processor. Lots of things do some trivial processing periodically, but can live with a slowed processor.)
This registers as a dynamic misc device, so it's usually char 10:63, but prints out what it's registered at during boot.
More information is available at http://www.nyx.net/~colin/ -- -Colin
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