kdump speed issues

Issue

• As we had always troubles to get reasonable fast dumps I took another attempt to figure out what's going on here.

• I did a "time dd if=/proc/vmcore of=/dev/null" to find out a maximum read performance with about 20MB/s.

• The kdump operation time of RHEL6 is much longer than RHEL5's one, because reading /proc/vmcore is slower on RHEL6.
• kdump(2nd kernel) in RHEL6.0 is much slower than that in RHEL5.5.

• I/O performance in which vmcore is collected by "core_collector cp":

  RHEL5.5: About 121.9MB/s
  RHEL6.0: About 12.2MB/s
  

• I/O performance in which vmcore is collected by "core_collector makedumpfile":

  RHEL5.5: About 118.7MB/s
  RHEL6.0: About 19.2MB/
  

• This is performance REGRESSION from RHEL5.5.