On Fri, 2 Mar 2007 17:40:04 -0800 William Lee Irwin III <[EMAIL PROTECTED]> wrote: >> My gut feeling is to agree, but I get nagging doubts when I try to >> think of how to boil things like [major benchmarks whose names are >> trademarked/copyrighted/etc. censored] down to simple testcases. Some >> other things are obvious but require vast resources, like zillions of >> disks fooling throttling/etc. heuristics of ancient downrev kernels.
On Fri, Mar 02, 2007 at 05:58:56PM -0800, Andrew Morton wrote: > noooooooooo. You're approaching it from the wrong direction. > Step 1 is to understand what is happening on the affected production > system. Completely. Once that is fully understood then it is a relatively > simple matter to concoct a test case which triggers the same failure mode. > It is very hard to go the other way: to poke around with various stress > tests which you think are doing something similar to what you think the > application does in the hope that similar symptoms will trigger so you can > then work out what the kernel is doing. yuk. Yeah, it's really great when it's possible to get debug info out of people e.g. they're willing to boot into a kernel instrumented with the appropriate printk's/etc. Most of the time it's all guesswork. People who post to lkml are much better about all this on average. I never truly understood the point of kprobes/jprobes/dprobes (or whatever the probing letter is), crash dumps, and so on until I ran into this, not that I use personally them (though I may yet start). Most of the time I just read the code instead and smoke out what could be going on by something like the process of devising counterexamples. For instance, I told that colouroff patch guy about the possibility of getting the wrong page for the start of the buffer from virt_to_page() on a cache colored buffer pointer (clearly cache->gfporder >= 4 in such a case). Deriving the head page without __GFP_COMP might be considered to be ugly-looking, though. -- wli - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/