hollalinux
/
linux-sg2042
mirror of https://github.com/sophgo/linux-riscv.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity

x86/boot/64: Optimize fixmap page fixup 

Single-stepping through head_64.S made me look at the fixmap page PTEs
fixup loop:

So we're going through the whole level2_fixmap_pgt 4K page, looking at
whether PAGE_PRESENT is set in those PTEs and add the delta between
where we're compiled to run and where we actually end up running.

However, if that delta is 0 (most cases) we go through all those 512
PTEs for no reason at all. Oh well, we add 0 but that's no reason to me.

Skipping that useless fixup gives us a boot speedup of 0.004 seconds in
my guest. Not a lot but considering how cheap it is, I'll take it. Here
is the printk time difference:

before:
  ...
  [    0.000000] tsc: Marking TSC unstable due to TSCs unsynchronized
  [    0.013590] Calibrating delay loop (skipped), value calculated using timer frequency..
		8027.17 BogoMIPS (lpj=16054348)
  [    0.017094] pid_max: default: 32768 minimum: 301
  ...

after:
  ...
  [    0.000000] tsc: Marking TSC unstable due to TSCs unsynchronized
  [    0.009587] Calibrating delay loop (skipped), value calculated using timer frequency..
		8026.86 BogoMIPS (lpj=16053724)
  [    0.013090] pid_max: default: 32768 minimum: 301
  ...

For the other two changes converting naked numbers to defines:

  # arch/x86/kernel/head_64.o:

   text    data     bss     dec     hex filename
   1124  290864    4096  296084   48494 head_64.o.before
   1124  290864    4096  296084   48494 head_64.o.after

md5:
   87086e202588939296f66e892414ffe2  head_64.o.before.asm
   87086e202588939296f66e892414ffe2  head_64.o.after.asm

Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20161125111448.23623-1-bp@alien8.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Borislav Petkov 2016-11-25 12:14:48 +01:00 committed by Ingo Molnar
parent 064025f7ea
commit 6248f45674
1 changed files with 6 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
arch/x86/kernel/head_64.S
View File

@ -147,6 +147,9 @@ startup_64:
decl %ecx decl %ecx
jnz 1b jnz 1b
test %rbp, %rbp
jz .Lskip_fixup
/* /*
* Fixup the kernel text+data virtual addresses. Note that * Fixup the kernel text+data virtual addresses. Note that
* we might write invalid pmds, when the kernel is relocated * we might write invalid pmds, when the kernel is relocated
@ -154,9 +157,9 @@ startup_64:
* beyond _end. * beyond _end.
*/ */
leaq level2_kernel_pgt(%rip), %rdi leaq level2_kernel_pgt(%rip), %rdi
leaq 4096(%rdi), %r8 leaq PAGE_SIZE(%rdi), %r8
/* See if it is a valid page table entry */ /* See if it is a valid page table entry */
1: testb $1, 0(%rdi) 1: testb $_PAGE_PRESENT, 0(%rdi)
jz 2f jz 2f
addq %rbp, 0(%rdi) addq %rbp, 0(%rdi)
/* Go to the next page */ /* Go to the next page */
@ -167,6 +170,7 @@ startup_64:
/* Fixup phys_base */ /* Fixup phys_base */
addq %rbp, phys_base(%rip) addq %rbp, phys_base(%rip)
.Lskip_fixup:
movq $(early_level4_pgt - __START_KERNEL_map), %rax movq $(early_level4_pgt - __START_KERNEL_map), %rax
jmp 1f jmp 1f
ENTRY(secondary_startup_64) ENTRY(secondary_startup_64)