Measuring Kernel Marker Overhead

Administrator · 10-07-2007, 05:38 PM

"It looks to be about 2.1% increase in time to do the make/mount/unmount operations with the marker patches in place and no blktrace operations," Alan Brunelle summarized some benchmarks testing the overhead of the kernel markers patches. He continued, "with the blktrace operations in place we see about a 3.8% decrease in time to do the same ops." Block layer maintainer Jens Axboe responded favorably, "thanks for running these numbers. I don't think you have to bother with it more. My main concern was a performance regression, increasing the overhead of running blktrace." He added, "I'd say the above is Good Enough for me," acking the kernel marker patches.

Jens went on to muse, "I do wonder about that performance _increase_ with blktrace enabled. I remember that we have seen and discussed something like this before, it's still a puzzle to me..." Mathieu Desnoyers agreed, "interesting question indeed," going on to suggest possible future tests to understand the unexpected performance increase. blktrace is a block layer IO tracing tool for providing detailed information about request queue operations, originally developed by Jens Axboe and merged into the mainline kernel in 2.6.17-rc1.