Hello, On Tue, Jun 28, 2016 at 06:46:34PM +0200, Rabin Vincent wrote: > On Tue, Jun 28, 2016 at 03:33:18PM +0900, Namhyung Kim wrote: > > On Tue, Jun 28, 2016 at 3:25 PM, Namhyung Kim <namhyung@xxxxxxxxxx> wrote: > > > I'm running some guest machines for kernel development. For debugging > > > purpose, I use lots of trace_printk() since it's faster than normal > > > printk(). When kernel crash happens the trace buffer is printed on > > > console (I set ftrace_dump_on_oops) but it takes too much time. I > > > don't want to reduce the size of ring buffer as I want to collect the > > > debug info as much as possible. And I also want to see trace from all > > > cpu so 'ftrace_dump_on_oop = 2' is not an option. > > > > > > I know the kexec/kdump (and the crash tool) can dump and analyze the > > > trace buffer later. But it's cumbersome to do it everytime and more > > > importantly, I don't want to spend the memory for the crashkernel. > > Assuming you're using QEMU: > > QEMU has a dump-guest-memory command which can be used to dump the > guest's entire memory to an ELF which can be loaded by the crash utility > to extract the trace buffer. This doesn't require kexec/kdump or any > other support from the guest kernel. Thanks for the info. Not requiring kexec/kdump step is a big win for me. Although I mostly use kvmtool (lkvm), I'll give it a try. > > It's apparently even possible to run QEMU with the guest memory in a > file and load that to crash directly, although this is not something > I've had a chance to try out myself: > > https://github.com/crash-utility/crash/commit/89ed9d0a7f7da4578294a492c1ad857244ce7352 Interesting, I'll take a look but wouldn't it impact the performance? And even if the crash tool is good, it'd be great if I can work without it (if possible). Thanks, Namhyung -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
