[PATCH 0/4] faster kexec reboot

[Albert Huang]

From: "huangjie.albert" <huangjie.albert at bytedance.com>

In many time-sensitive scenarios, we need a shorter time to restart 
the kernel. However, in the current kexec fast restart code, there 
are many places in the memory copy operation, verification operation 
and decompression operation, which take more time than 500ms. Through 
the following patch series. machine_kexec-->start_kernel only takes 15ms

How to measure time:

c code:
uint64_t current_cycles(void)
{
    uint32_t low, high;
    asm volatile("rdtsc" : "=a"(low), "=d"(high));
    return ((uint64_t)low) | ((uint64_t)high << 32);
}
assembly code:
       pushq %rax
       pushq %rdx
       rdtsc
       mov   %eax,%eax
       shl   $0x20,%rdx
       or    %rax,%rdx
       movq  %rdx,0x840(%r14)
       popq  %rdx
       popq  %rax
the timestamp may store in boot_params or kexec control page, so we can
get the all timestamp after kernel boot up.

huangjie.albert (4):
  kexec: reuse crash kernel reserved memory for normal kexec
  kexec: add CONFING_KEXEC_PURGATORY_SKIP_SIG
  x86: Support the uncompressed kernel to speed up booting
  x86: boot: avoid memory copy if kernel is uncompressed

 arch/x86/Kconfig                   | 10 +++++++++
 arch/x86/boot/compressed/Makefile  |  5 ++++-
 arch/x86/boot/compressed/head_64.S |  8 +++++--
 arch/x86/boot/compressed/misc.c    | 35 +++++++++++++++++++++++++-----
 arch/x86/purgatory/purgatory.c     |  7 ++++++
 include/linux/kexec.h              |  9 ++++----
 include/uapi/linux/kexec.h         |  2 ++
 kernel/kexec.c                     | 19 +++++++++++++++-
 kernel/kexec_core.c                | 16 ++++++++------
 kernel/kexec_file.c                | 20 +++++++++++++++--
 scripts/Makefile.lib               |  5 +++++
 11 files changed, 114 insertions(+), 22 deletions(-)

-- 
2.31.1