diff --git a/kexec-kdump-howto.txt b/kexec-kdump-howto.txt index 05b497f..b4cdc22 100644 --- a/kexec-kdump-howto.txt +++ b/kexec-kdump-howto.txt @@ -616,6 +616,37 @@ options are copied from /proc/cmdline. In general it is best to append command line options using "KDUMP_COMMANDLINE_APPEND=" instead of replacing the original command line completely. +Parallel Dumping Operation +========================== +Kexec allows kdump using multiple cpus. So parallel feature can accelerate +dumping substantially, especially in executing compression and filter. +For example: + + 1."makedumpfile -c --num-threads [THREAD_NUM] /proc/vmcore dumpfile" + 2."makedumpfile -c /proc/vmcore dumpfile", + + 1 has better performance than 2, if THREAD_NUM is larger than two + and the usable cpus number is larger than THREAD_NUM. + +Notes on how to use multiple cpus on a capture kernel on x86 system: + +Make sure that you are using a kernel that supports disable_cpu_apicid +kernel option as a capture kernel, which is needed to avoid x86 specific +hardware issue (*). The disable_cpu_apicid kernel option is automatically +appended by kdumpctl script and is ignored if the kernel doesn't support it. + +You need to specify how many cpus to be used in a capture kernel by specifying +the number of cpus in nr_cpus kernel option in /etc/sysconfig/kdump. nr_cpus +is 1 at default. + +You should use necessary and sufficient number of cpus on a capture kernel. +Warning: Don't use too many cpus on a capture kernel, or the capture kernel +may lead to panic due to Out Of Memory. + +(*) Without disable_cpu_apicid kernel option, capture kernel may lead to +hang, system reset or power-off at boot, depending on your system and runtime +situation at the time of crash. + Debugging Tips -------------- - One can drop into a shell before/after saving vmcore with the help of