Dear everyone, I'm trying to trace some syscalls in Debian Jessie, that's the distro kernel 3.16.0-4-amd64 . My motivation is to trace manipulations / forced adjustments of the system timebase: ntpd, ntpdate, date -s or some such. I've figured out most of the stuff already, I guess. The lines are too long for an e-mail body - I'm attaching a sample of what I'm doing, in a file called "tracing.txt" (UNIX EOLs). What strikes me: even if I enable just six individual "events", in the trace buffer (output) I get a waterfall of unrelated events being logged - looks like routine process scheduler clockwork. See the attached havoc.txt. Is it fruitful to capture those events in the first place, only to have to filter most of it away? I haven't found a way to prevent actual tracing of those events, I can only filter them from being logged (which sounds like a second stage after capturing). Filtering the trace output works in the sense that I only get the interesting syscalls in my trace, but actually capturing all the process scheduler fuss in the background feels like a lot of unnecessary CPU load, which might be a problem on a busy machine, or on a machine trying to do its best at timekeeping... Is this a "feature" of this relatively old debianese kernel? Is there a way to prevent capturing the scheduler events, by way of some simple configuration? I haven't tried a newer or vanilla kernel... does it still work the same way in more modern kernels? BTW, marvellous job on the tracing infrastructure... kudos. This is like strace on steroids. Actually I've just used strace to find out what syscalls I should be watching in the kernel in the first place :-) Any ideas are welcome, and have a nice day everybody :-) Frank Rysanek
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Date: 27 Apr 2017, 0:39
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