Hi - On Sat, Dec 07, 2013 at 08:19:13AM +0900, Masami Hiramatsu wrote:
> [...] > > Would you plan to limit kprobes (or just the perf-probe frontend) to > > only function-entries also? > Exactly, yes :). Currently I have a patch for kprobe-tracer > implementation (not only for perf-probe, but doesn't limit kprobes > itself). Interesting option. It sounds like a restrictive expedient that could result in kprobes never being made sufficiently robust. > > If not, and if intra-function statement-granularity kprobes remain > > allowed within a function-granularity whitelist, then you might > > still have those "quantitative" problems. > Yes, but as far as I've tested, the performance overhead is not > high, especially as far as putting kprobes at the entry of those > functions because of ftrace-based optimization. (Would that also make CONFIG_KPROBE_EVENT require KPROBES_ON_FTRACE?) > > Even worse, kprobes robustness problems can bite even with a small > > whitelist, unless you can test the countless subset selections > > cartesian-product the aggrevating factors (like other tracing > > facilities being in use at the same time, limited memory, high irq > > rates, debugging sessions, architectures, whatever). > > And also, what script will run on each probe, right? :) In the perf-probe world, the closest analogue could be varying the contextual data that's being extracted (stack traces, parameters, ...). > >> [...] For the long term solution, I think we can introduce some > >> kind of performance gatekeeper as systemtap does. Counting the > >> miss-hit rate per second and if it go over a threshold, disable next > >> miss-hit (or most miss-hit) probe (as OOM killer does). > > > > That would make sense, but again it would not help deal with kprobes > > robustness (in the kernel-crashing rather than kernel-slowdown sense). > > Why would you think so? Is there any hidden path for calling kprobes > mechanism?? The kernel crash problem just comes from bugs, not the > quantitative issue. I don't think we're disagreeing. A performance-gatekeeper in perf-probe or nearby would be useful (and manage the kprobe-quantity problem). It would not be sufficient to prevent the kernel-crashing bugs. - FChE -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
