Commit-ID: 6248f4567442081994ad61c63bd9870e147983e0 Gitweb: http://git.kernel.org/tip/6248f4567442081994ad61c63bd9870e147983e0 Author: Borislav Petkov <bp@xxxxxxx> AuthorDate: Fri, 25 Nov 2016 12:14:48 +0100 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitDate: Mon, 28 Nov 2016 07:45:17 +0100 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@xxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Brian Gerst <brgerst@xxxxxxxxx> Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx> Cc: H. Peter Anvin <hpa@xxxxxxxxx> Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Link: http://lkml.kernel.org/r/20161125111448.23623-1-bp@xxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> --- arch/x86/kernel/head_64.S | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S index b4421cc..a4a814f 100644 --- a/arch/x86/kernel/head_64.S +++ b/arch/x86/kernel/head_64.S @@ -147,6 +147,9 @@ startup_64: decl %ecx jnz 1b + test %rbp, %rbp + jz .Lskip_fixup + /* * Fixup the kernel text+data virtual addresses. Note that * we might write invalid pmds, when the kernel is relocated @@ -154,9 +157,9 @@ startup_64: * beyond _end. */ leaq level2_kernel_pgt(%rip), %rdi - leaq 4096(%rdi), %r8 + leaq PAGE_SIZE(%rdi), %r8 /* See if it is a valid page table entry */ -1: testb $1, 0(%rdi) +1: testb $_PAGE_PRESENT, 0(%rdi) jz 2f addq %rbp, 0(%rdi) /* Go to the next page */ @@ -167,6 +170,7 @@ startup_64: /* Fixup phys_base */ addq %rbp, phys_base(%rip) +.Lskip_fixup: movq $(early_level4_pgt - __START_KERNEL_map), %rax jmp 1f ENTRY(secondary_startup_64) -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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