Ktap almost gets into 3.13

Posted Nov 12, 2013 3:58 UTC (Tue) by bgregg (guest, #46639)
In reply to: Ktap almost gets into 3.13 by lambda
Parent article: Ktap almost gets into 3.13

perf is great. I've used it's profiling (sampling), static tracing, and dynamic tracing abilities, and with access to local variables. And I've written and shared documentation about perf (conference talks, books).

pref can do a lot, but there are some things where the performance hit can make me hesitate. For example, timing a busy kernel function, where I'm interested in examining its distribution, to identify outliers or multiple modes. perf has an enable/trace/dump/post-process cycle to get to the answer I want. ktap (and DTrace and SystemTap) can execute arbitrary programs in kernel context, where it can filter and summarize using per-CPU buffers (eg, via kp_percpu_data()), and then emit an answer without making a trip to user-level to post-process data. It can also (more easily) let me build real time tools.

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Ktap almost gets into 3.13

Posted Nov 13, 2013 20:35 UTC (Wed) by karim (subscriber, #114) [Link]

Hi Brendan (assuming this is Brendan Gregg),

Yes, it's been a pleasure watching the videos of some of those talks and I'm glad to see your "System Performance" title is finally out, I've been waiting for it for a while. Time to order a copy.

FWIW, I'm not saying perf is useless. Just that it doesn't do what I need. Then again, as I said, I'm not the typical user: I wrote LTT in the late '90s and maintained it for a few years. That doesn't necessarily make my opinion worth more than what others have to say, but I do have a fairly good handle on what such tools can be capable of and we're certainly not where we should be and my expectations, based on historical record, are fairly low.